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Objectives Hemoglobin A1c (HbA1c) is a valuable parameter in the monitoring of diabetic patients and increasingly in diagnosis of diabetes. Manufacturers continuously optimize instruments, currently the main focus is to achieve faster turnaround times. It is important that performance specifications remain of high enough standard, which is evaluated in this study for the new ARKRAY HA-8190V instrument. Methods The Clinical and Laboratory Standards Institute (CLSI) protocols EP-5, EP-9 and EP-10 were applied to investigate imprecision, bias and linearity. In addition potential interferences, performance in External Quality Assessment (EQA) and performance against the HA-8180V instrument in 220 clinical samples was evaluated. Results The HA-8190V demonstrates a CV of ≤0.8% in IFCC SI units (≤0.6% National Glycohemoglobin Standardization Program [NGSP]) at 34 and 102 mmol/mol levels (5.3 and 11.5% NGSP) and a bias of −0.1 mmol/mol (−0.01% NGSP) at a concentration of 50 mmol/mol (6.7% NGSP), but with a significant slope as compared to target values. This results in a bias of −1.0 and 0.9 mmol/mol (−2.0 and 0.9% NGSP) at the 30 and 70 mmol/mol (4.9 and 8.6% NGSP) concentration level. Simulation of participation in the IFCC certification programme results in a Silver score (bias −0.1 mmol/mol, CV 1.1%). Interference in the presence of the most important Hb variants (AS, AC, AE, AD) and elevated HbA2 and HbF concentrations is less than 3 mmol/mol (0.3% NGSP) at a concentration of 50 mmol/mol (6.7% NGSP). Conclusions Analytical performance of the HA-8190V is very good, especially with respect to precision and HbA1c quantification in the presence of the most common Hb variants.

Establishing metrological traceability to an assigned value of a matrix-based certified reference material (CRM) that has been validated to be commutable among available end-user measurement procedures (MPs) is central to producing equivalent results for the measurand in clinical samples (CSs) irrespective of the clinical laboratory MPs used. When a CRM is not commutable with CSs, the bias due to noncommutability will be propagated to the CS results causing incorrect metrological traceability to the CRM and nonequivalent CS results among different MPs. In a commutability assessment, a conclusion that a CRM is commutable or noncommutable for use with a specific MP is made when the difference in bias between the CRM and CSs meets or does not meet a criterion for that specific MP when compared to other MPs. A conclusion regarding commutability or noncommutability requires that the magnitude of the difference in bias observed in the commutability assessment remains unchanged over time. This conclusion requires the CRM to be stable and no substantive changes in the MPs. These conditions should be periodically reverified. If an available CRM is determined to be noncommutable for a specific MP, that CRM can be used in the calibration hierarchy for that MP when an appropriately validated MP-specific correction for the noncommutability bias is included. We describe with examples how a MP-specific correction and its uncertainty can be developed and applied in a calibration hierarchy to achieve metrological traceability of results for CSs to the CRM’s assigned value. BACKGROUND: TERMINOLOGY FOR MEASUREMENT PROCEDURE, MEASURING SYSTEM, AND IN VITRO DIAGNOSTIC MEDICAL DEVICE: As explained in part 1 of this series (1), we use the term measurement procedure (MP) when referring to a written specification for equipment, reagents, calibrators, and other components for making a measurement. We use the term in vitro diagnostic medical device (IVD-MD) for a physical measuring system manufactured according to the MP specifications and used to make measurements on clinical samples (CSs). An IVD-MD can be manufactured by a commercial company or by a clinical laboratory for its own use as a laboratory developed test.

Objectives Hepcidin measurement advances insights in pathophysiology, diagnosis, and treatment of iron disorders, but requires analytically sound and standardized measurement procedures (MPs). Recent development of a two-level secondary reference material (sRM) for hepcidin assays allows worldwide standardization. However, no proficiency testing (PT) schemes to ensure external quality assurance (EQA) exist and the absence of a high calibrator in the sRM set precludes optimal standardization. Methods We developed a pilot PT together with the Dutch EQA organization Stichting Kwaliteitsbewaking Medische Laboratoriumdiagnostiek (SKML) that included 16 international hepcidin MPs. The design included 12 human serum samples that allowed us to evaluate accuracy, linearity, precision and standardization potential. We manufactured, value-assigned, and validated a high-level calibrator in a similar manner to the existing low- and middle-level sRM. Results The pilot PT confirmed logistical feasibility of an annual scheme. Most MPs demonstrated linearity (R2>0.99) and precision (duplicate CV>12.2%), although the need for EQA was shown by large variability in accuracy. The high-level calibrator proved effective, reducing the inter-assay CV from 42.0% (unstandardized) to 14.0%, compared to 17.6% with the two-leveled set. The calibrator passed international homogeneity criteria and was assigned a value of 9.07±0.24 nmol/L. Conclusions We established a framework for future PT to enable laboratory accreditation, which is essential to ensure quality of hepcidin measurement and its use in patient care. Additionally, we showed optimized standardization is possible by extending the current sRM with a third high calibrator, although international implementation of the sRM is a prerequisite for its success.

Objectives External quality assessment (EQA) with commutable samples is used for assessing agreement of results for patients’ samples. We investigated the feasibility to aggregate results from four different EQA schemes to determine the bias between different measurement procedures and a reference target value. Methods We aggregated EQA results for creatinine from programs that used commutable EQA material by calculating the relative difference between individual participant results and the reference target value for each sample. The means and standard errors of the means were calculated for the relative differences. Results were partitioned by methods, manufacturers and instrument platforms to evaluate the biases for the measurement procedures. Results Data aggregated for enzymatic methods had biases that varied from −8.2 to 3.8% among seven instrument platforms for creatinine at normal concentrations (61–85 μmol/L). EQA schemes differed in the evidence provided about the commutability of their samples, and in the amount of detail collected from participants regarding the measurement procedures which limited the ability to sub-divide aggregated data by instrument platforms and models. Conclusions EQA data could be aggregated from four different programs using different commutable samples to determine bias among different measurement procedures. Criteria for commutability for EQA samples as well as standardization of reporting the measurement methods, reagents, instrument platforms and models used by participants are needed to improve the ability to aggregate the results for optimal assessment of performance of measurement procedures. Aggregating data from a larger number of EQA schemes is feasible to assess trueness on a global scale.

Background Hepcidin concentrations measured by various methods differ considerably, complicating interpretation. Here, a previously identified plasma-based candidate secondary reference material (csRM) was modified into a serum-based two-leveled sRM. We validated its functionality to increase the equivalence between methods for international standardization. Methods We applied technical procedures developed by the International Consortium for Harmonization of Clinical Laboratory Results. The sRM, consisting of lyophilized serum with cryolyoprotectant, appeared commutable among nine different measurement procedures using 16 native human serum samples in a first round robin (RR1). Harmonization potential of the sRM was simulated in RR1 and evaluated in practice in RR2 among 11 measurement procedures using three native human plasma samples. Comprehensive purity analysis of a candidate primary RM (cpRM) was performed by state of the art procedures. The sRM was value assigned with an isotope dilution mass spectrometry-based candidate reference method calibrated using the certified pRM. Results The inter-assay CV without harmonization was 42.1% and 52.8% in RR1 and RR2, respectively. In RR1, simulation of harmonization with sRM resulted in an inter-assay CV of 11.0%, whereas in RR2 calibration with the material resulted in an inter-assay CV of 19.1%. Both the sRM and pRM passed international homogeneity criteria and showed long-term stability. We assigned values to the low (0.95±0.11 nmol/L) and middle concentration (3.75±0.17 nmol/L) calibrators of the sRM. Conclusions Standardization of hepcidin is possible with our sRM, which value is assigned by a pRM. We propose the implementation of this material as an international calibrator for hepcidin.

Background Diabetes mellitus is a major global issue and high quality testing is essential for the diagnosis and treatment of the disease. The IFCC Committee for the Education in the Utility of Biomarkers in Diabetes (C-EUBD) plays a global role in improving knowledge and understanding around diabetes testing. This paper describes a multi-stakeholder approach, to improving diagnostic and therapeutic testing for diabetes, using a multicentre study in China as an example of the global impact of the group. Methods Educational workshops were developed to support the scientific aims of the study in which 30 centres around China received identical, fresh frozen whole blood samples with values assigned using IFCC secondary reference methods and undertook precision (EP-5) and trueness studies. Performance was assessed using sigma metrics. Results A successful multi-stakeholder group was developed and sustained throughout the study through several educational workshops, which enabled the formation of a long-term collaboration with key opinion leaders and policy makers in China. All 30 centres showed good performance with within and between laboratory coefficient of variations (CVs) below 3% in SI units at both low and high haemoglobin A1c (HbA1c) levels. All individual laboratories met the criteria of a sigma of two or more at a total allowable error (TAE) of 5 mmol/mol (0.46% NGSP). Conclusions The study led to a successful multi-partner approach to improving diabetes testing in China. All centres involved in the study meeting the published IFCC quality criteria, paving the way for future clinical trials and an expanded role for HbA1c testing across the country.

A process is described to assess the commutability of a reference material (RM) intended for use as a calibrator, trueness control, or external quality assessment sample based on the difference in bias between an RM and clinical samples (CSs) measured using 2 different measurement procedures (MPs). This difference in bias is compared with a criterion based on a medically relevant difference between an RM and CS results to make a conclusion regarding commutability. When more than 2 MPs are included, the commutability is assessed pairwise for all combinations of 2 MPs. This approach allows the same criterion to be used for all combinations of MPs included in the assessment. The assessment is based on an error model that allows estimation of various random and systematic sources of error, including those from sample-specific effects of interfering substances. An advantage of this approach is that the difference in bias between an RM and the average bias of CSs at the concentration (i.e., amount of substance present or quantity value) of the RM is determined and its uncertainty estimated. An RM is considered fit for purpose for those MPs for which commutability is demonstrated.

A process is described to assess the commutability of a reference material (RM) intended for use as a calibrator based on its ability to fulfill its intended use in a calibration traceability scheme to produce equivalent clinical sample (CS) results among different measurement procedures (MPs) for the same measurand. Three sources of systematic error are elucidated in the context of creating the calibration model for translating MP signals to measurand amounts: calibration fit, calibrator level trueness, and commutability. An example set of 40 CS results from 7 MPs is used to illustrate estimation of bias and variability for each MP. The candidate RM is then used to recalibrate each MP, and its effectiveness in reducing the systematic error among the MPs within an acceptable level of equivalence based on medical requirements confirms its commutability for those MPs. The RM is declared noncommutable for MPs for which, after recalibration, the CS results do not agree with those from other MPs. When a lack of agreement is found, other potential causes, including lack of calibration fit, should be investigated before concluding the RM is noncommutable. The RM is considered fit for purpose for those MPs where commutability is demonstrated.

Calibration 2.000 was initiated 20 years ago for standardization and harmonization of medical tests. The program also intended to evaluate adequate implementation of the In Vitro Diagnostics (IVD) 98/79/EC directive, in order to ensure that medical tests are fit-for-clinical purpose. The Calibration 2.000 initiative led to ongoing verification of test standardization and harmonization in the Netherlands using commutable external quality assessment (EQA)-tools and a type 1 EQA-design, where feasible. National support was guaranteed by involving all laboratory professionals as well as laboratory technicians responsible for EQA and quality officers. A category 1 EQA-system for general chemistry analytes, harmonizers for specific analytes like hGH and IGF-1, and commutable materials for other EQA-sections have been developed and structurally introduced in the EQA-schemes. The type 1 EQA-design facilitates the dialogue between individual specialists in laboratory medicine and the IVD-industry to reduce lot-to-lot variation and to improve standardization. In such a way, Calibration 2.000 sheds light on the metrological traceability challenges that we are facing and helps the laboratory community to get the issues on the table and resolved. The need for commutable trueness verifiers and/or harmonizers for other medical tests is now seen as paramount. Much knowledge is present in the Netherlands and for general chemistry, humoral immunology and protein chemistry, a few endocrinology tests, and various therapeutic drug monitoring (TDM) tests, commutable materials are available. Also the multi sample evaluation scoring system (MUSE) and the category 1 EQA-design offer many possibilities for permanent education of laboratory professionals to further improve the between and within laboratory variation and the test equivalence.

Measurements of inorganic elements in clinical laboratories produce results used for the diagnosis, the treatment and the monitoring of deficiencies or overloads. The main objective of External Quality Assessment Schemes is to verify, on a regular frequency, that clinical laboratory results correspond to the quality requirement for patient care. Therefore, External Quality Assessment Schemes represent an essential component of a laboratory's quality management system. However, External Quality Assessment Schemes within the same analytical field remain heterogeneous for different reasons such as samples, determination of assigned value, acceptable limits, content of the reports. The aim of this review was to describe and illustrate some major critical aspects of External Quality Assessment Schemes based on Occupational and Environmental Laboratory Medicine external quality assessment scheme experience.

Post-vaccination testing after hepatitis B vaccination is indispensable to evaluate long-term immunological protection. Using a threshold level of antibodies against hepatitis B surface antigen (anti-HBs) to define serological protection, implies reproducible and valid measurements of different diagnostic assays.In this study we assess the performance of currently used anti-HBs assays.In 2013, 45 laboratories participated in an external quality assessment program using pooled anti-HBs serum samples around the cutoff values 10IU/l and 100IU/l. Laboratories used either Axsym (Abbott Laboratories), Architect (Abbott Laboratories), Access (Beckman-Coulter), ADVIA Centaur anti-HBs2 (Siemens Healthcare Diagnostics), Elecsys, Modular or Cobas (Roche Diagnostics) or Vidas Total Quick (Biomerieux) for anti-HBs titre quantification. We analysed covariance using mixed-model repeated measures. To assess sensitivity/specificity and agreement, a true positive or true negative result was defined as an anti-HBs titre respectively above or below the cutoff value by ≥4 of 6 assays.Different anti-HBs assays were associated with statistically significant (P0.05) differences in anti-HBs titres in all dilutions. Sensitivity and specificity ranged respectively from 64%-100% and 95%-100%. Agreement between assays around an anti-HBs titre cutoff value of 10IU/l ranged from 93%-100% and was 44% for a cutoff value of 100IU/l.Around a cutoff value of 10IU/l use of the Access assay may result in false-negative results. Concerning the cutoff value of 100IU/l, a sample being classified below or above this cutoff relied heavily on the specific assay used, with both the Architect and the Access resulting in false-negative results.

Background: External quality assessment/proficiency test (EQA/PT) organizers play an important role in monitoring the performance of HbA1c measurements. With increasing quality of the assays, HbA1c is increasingly used for diagnosis of diabetes and the demands on EQA/PT organizers themselves are rising constantly. EQA organizers in Germany (INSTAND), Belgium (WIV/IPV), and the Netherlands (SKML) organized a program with commutable samples and target values assigned with the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) reference system. The aim of this project was to confirm the logistic feasibility of organizing synchronically in the three countries, an accuracy-based EQA program with fresh whole blood, to investigate the performance of HbA1c assays within and across countries and manufacturers, and to review the EQA acceptance limits. Methods: Throughout 2015, ten fresh whole blood samples were supplied to the participants. Aggregated results were evaluated according to the IFCC model for quality targets at four levels: overall, per country, per manufacturer, and per country per manufacturer. Results: Robust results in summer and winter demonstrated the feasibility of organizing an EQA with fresh whole blood samples in three countries. The overall performances, as well as the performance for each country were very similar: results fell within the IFCC criteria. Although substantial differences between results from different manufacturers were present, the performances of laboratories using tests of the same manufacturer were strikingly similar in the three countries, suggesting that the quality of HbA1c assays is for the most part manufacturer- related. The improved design of the EQA program also suggested that acceptance limits for performance can be reduced to approximately 8%.

BACKGROUND A major objective of the IFCC Committee on Education and Use of Biomarkers in Diabetes is to generate awareness and improvement of HbA1c assays through evaluation of the performance by countries and manufacturers. METHODS Fresh whole blood and lyophilized hemolysate specimens manufactured from the same pool were used by 17 external quality assessment organizers to evaluate analytical performance of 2166 laboratories. Results were evaluated per country, per manufacturer, and per manufacturer and country combined according to criteria of the IFCC model for quality targets. RESULTS At the country level with fresh whole blood specimens, 6 countries met the IFCC criterion, 2 did not, and 2 were borderline. With lyophilized hemolysates, 5 countries met the criterion, 2 did not, and 3 were borderline. At the manufacturer level using fresh whole blood specimens, 13 manufacturers met the criterion, 8 did not, and 3 were borderline. Using lyophilized hemolysates, 7 manufacturers met the criterion, 6 did not, and 3 were borderline. In both country and manufacturer groups, the major contribution to total error derived from between-laboratory variation. There were no substantial differences in performance between groups using fresh whole blood or lyophilized hemolysate samples. CONCLUSIONS The state of the art is that 1 of 20 laboratories does not meet the IFCC criterion, but there are substantial differences between country and between manufacturer groups. Efforts to further improve quality should focus on reducing between-laboratory variation. With some limitations, fresh whole blood and well-defined lyophilized specimens are suitable for purpose.

Background Accurate measurements of rheumatoid factors (RFs), autoantibodies binding IgG, are important for diagnosing rheumatoid arthritis (RA) and for predicting disease course. Worldwide, various RF assays are being used that differ in technique and target antigens. Objectives To study whether assay choice leads to clinically important discrepancies in RF status and level. Methods RF measurements using 4 commercial RF assays were compared in 32 RF + samples. Using ELISAs, the influence of the target antigen source—human IgG (hIgG) versus rabbit IgG (rIgG)—on measured RF levels was investigated in arthralgia patients and RA patients. Results Substantial discrepancies were found between RF levels measured in the four commercial assays. 6 samples (19%) with RF levels below or slightly above the cut-off in an rIgG-based assay were RF + in three assays using hIgG as the target antigen, some with very high levels. Direct ELISA comparisons of RF reactivity against hIgG and rIgG estimated that among 173 ACPA + arthralgia patients, originally RF negative in rIgG-based assays, up to 10% were single positive against hIgG. Monoclonal RFs binding to hIgG and rIgG or hIgG only supported these findings. In a cohort of 69 early RA patients, virtually all RF responses reacted with both targets, although levels were still variable. Conclusions The use of RF assays that differ in technique and target antigen, together with the different specificities of RF responses, leads to discrepancies in RF status and levels. This has important consequences for patient care if RA diagnosis and disease progression assessments are based on RF test results. Disclosure of Interest None declared

The aim of this study was to compare different analytical methods that are currently in use in the Netherlands for the measurement of whole blood vitamin B6.This method comparison study consisted of two separate parts. (1) Four laboratories participated in a pilot study in which the commercial Chromsystems and INstruchemie method, and a laboratory developed liquid chromatography-tandem mass spectrometry (LC-MS/MS) method and HPLC method were compared. Sixty-nine frozen whole blood samples and six lyophilized whole blood samples were used for comparison. (2) In the nationwide part of the study, 49 laboratories participated in the analysis of three identical sets of two whole blood samples of which one set was freshly analyzed, one set was analyzed after storage at −20 °C and one set was analyzed after lyophilization.In both parts of the study, the HPLC and LC-MS/MS methods showed equivalent results for all sample types tested. The Chromsystems method showed a positive bias of 45% (pilot study) and 30% (nationwide study) towards the LC-MS/MS method when fresh or frozen samples were used. The measurement of lyophilized samples showed no differences between the methods. The results of the INstruchemie method were inconclusive due to the low number of participants.The different analytical methods for measuring vitamin B6 produce different results when whole blood patient samples are measured. The recognition of a reference method or the development of suitable reference materials and quality control materials might serve as a first step towards improved standardization or harmonization of the whole blood vitamin B6 assay.

Commutability is a property of a reference material (RM) that relates to the closeness of agreement between results for an RM and results for clinical samples (CSs) when measured by ≥2 measurement procedures (MPs). Commutability of RMs used in a calibration traceability scheme is an essential property for them to be fit for purpose. Similarly, commutability of trueness controls or external quality assessment samples is essential when those materials are used to assess trueness of results for CSs. This report is part 1 of a 3-part series describing how to assess commutability of RMs. Part 1 defines commutability and addresses critical components of the experimental design for commutability assessment, including selection of individual CSs, use of pooled CSs, qualification of MPs for inclusion, establishing criteria for the determination that an RM is commutable, generalization of commutability conclusions to future measurements made with the MPs included in the assessment, and information regarding commutability to be included in the certificate for an RM. Parts 2 and 3 in the series present 2 different statistical approaches to commutability assessment that use fixed criteria related to the medical decisions that will be made using the laboratory test results.

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HbA1c is a key parameter in diabetes management. For years the test has been used exclusively for monitoring of long-term diabetic control. However, due to improvement of the performance, HbA1c is considered more and more for diagnosis and screening. With this new application, quality demands further increase. A task force of the International Federation of Clinical Chemistry and Laboratory Medicine developed a model to set and evaluate quality targets for HbA1c. The model is based on the concept of total error and takes into account the major sources of analytical errors in the medical laboratory: bias and imprecision. Performance criteria are derived from sigma-metrics and biological variation. This review shows 2 examples of the application of the model: at the level of single laboratories, and at the level of a group of laboratories. In the first example data of 125 individual laboratories of a recent external quality assessment program in the Netherlands are evaluated. Differences between laboratories as well as their relation to method principles are shown. The second example uses recent and 3-year-old data of the proficiency test of the College of American Pathologists. The differences in performance between 26 manufacturer-related groups of laboratories are shown. Over time these differences are quite consistent although some manufacturers improved substantially either by better standardization or by replacing a test. The IFCC model serves all who are involved in HbA1c testing in the ongoing process of better performance and better patient care.

Background: Accurate measurements of rheumatoid factors (RFs), autoantibodies binding IgG, are important for diagnosing rheumatoid arthritis (RA) and for predicting disease course. Worldwide, various RF assays are being used that differ in technique and target antigens. We studied whether assay choice leads to clinically important discrepancies in RF status and level. Methods: RF measurements using four commercial RF assays were compared in 32 RF+ samples. Using enzyme-linked immunosorbent assays (ELISAs), the influence of the target antigen source – human IgG (hIgG) versus rabbit IgG (rIgG) – on measured RF levels was investigated in arthralgia patients and RA patients. Results: Substantial discrepancies were found between RF levels measured in the four commercial assays. Six samples (19%) with RF levels below or slightly above the cutoff in the rIgG-based Phadia assay were RF+ in three assays using hIgG as the target antigen, some with very high levels. Direct ELISA comparisons of RF reactivity against hIgG and rIgG estimated that among 173 ACPA+ arthralgia patients, originally RF negative in rIgG-based assays, up to 10% were single positive against hIgG. Monoclonal RFs binding to hIgG and rIgG or hIgG only supported these findings. In a cohort of 69 early RA patients, virtually all RF responses reacted with both targets, although levels were still variable. Conclusions: The use of RF assays that differ in technique and target antigen, together with the different specificities of RF responses, leads to discrepancies in RF status and levels. This has important consequences for patient care if RA diagnosis and disease progression assessments are based on RF test results.

IntroductionReliable serum creatinine measurements are of vital importance for the correct classification of chronic kidney disease and early identification of kidney injury. The National Kidney Disease Education Programme working group and other groups have defined clinically acceptable analytical limits for creatinine methods. The aim of this study was to re-evaluate the performance of routine creatinine methods in the light of these defined limits so as to assess their suitability for clinical practice.MethodIn collaboration with the Dutch External Quality Assurance scheme, six frozen commutable samples, with a creatinine concentration ranging from 80 to 239 μmol/L and traceable to isotope dilution mass spectrometry, were circulated to 91 laboratories in four European countries for creatinine measurement and estimated glomerular filtration rate calculation. Two out of the six samples were spiked with glucose to give high and low final concentrations of glucose.ResultsResults from 89 laboratories were analysed for bias, imprecision (%CV) for each creatinine assay and total error for estimated glomerular filtration rate. The participating laboratories used analytical instruments from four manufacturers; Abbott, Beckman, Roche and Siemens. All enzymatic methods in this study complied with the National Kidney Disease Education Programme working group recommended limits of bias of 5% above a creatinine concentration of 100 μmol/L. They also did not show any evidence of interference from glucose. In addition, they also showed compliance with the clinically recommended %CV of ≤4% across the analytical range. In contrast, the Jaffe methods showed variable performance with regard to the interference of glucose and unsatisfactory bias and precision.ConclusionJaffe-based creatinine methods still exhibit considerable analytical variability in terms of bias, imprecision and lack of specificity, and this variability brings into question their clinical utility. We believe that clinical laboratories and manufacturers should work together to phase out the use of relatively non-specific Jaffe methods and replace them with more specific methods that are enzyme based.

Proficiency testing schemes monitor laboratory performance and provide a stimulus for improvement in accuracy. Where several schemes operate in the same analytical sector, there are risks that assessments of performance may be in conflict. Performance assessment for the determination of trace elements such as aluminum in serum is particularly important due to the high risk of contamination and therefore erroneous results. The objectives of this work were (1) to compare several mathematical models to establish a predefined standard deviation for proficiency assessment and (2) to evaluate the influence of instrumental methods and proficiency testing scheme on the assessment of performance for serum aluminum measurements. For this purpose, three samples were sent to the participants of four proficiency testing schemes. Assigned values were calculated according to algorithm A according to ISO 13528 and standard deviation for proficiency assessment according to three methods based on individual variability, state of the art or previous proficiency testing results. The method based on individual variability produced a more stringent standard deviation compared to analytical imprecision based on the state of the art. The instrumental methods gave similar results, whereas significant differences were observed between the four proficiency testing schemes indicating that harmonization of the standard deviation for proficiency assessment fails to allow transferability from one proficiency testing scheme to another and that additional factor(s) contribute to variability in performance assessment.

After the relationship between glycemic control and the HbA1c concentration was demonstrated, many tests have been developed to determine the HbA1c concentration. The test results are standardized to the International Federation of Clinical Chemistry (IFCC) Reference Measurement Procedure (RMP) in harmony with the efforts of the National Glycohemoglobin Standardization Program (NGSP). The longitudinal use of the test requires strict quality management including accreditation of the laboratory, a dedicated internal control design, participation in an external quality assessment (EQA) program (proficiency test), and careful consideration of pre- and post-analytical aspects of the test. Performance goals for optimizing determination of the HbA1c concentration have been described. As an index of long-term glycemic control and a risk predictor, the HbA1c concentration is an indispensable part of routine management of diabetes. Because of the improving quality of the test, the HbA1c concentration is being increasingly applied in the diagnosis of diabetes. There are, however, concerns of this application in point-of-care settings. The HbA1c concentration is also used to achieve stringent control in pregnant diabetic patients. Strict standardization enables the definition of universal reference values and clinical decision limits. This review describes the present status of analytical and clinical aspects of determining the HbA1c concentration and highlights the challenges involved.

Background: Optimum patient care in relation to laboratory medicine is achieved when results of laboratory tests are equivalent, irrespective of the analytical platform used or the country where the laboratory is located. Standardization and harmonization minimize differences and the success of efforts to achieve this can be monitored with international category 1 external quality assessment (EQA) programs. Methods: An EQA project with commutable samples, targeted with reference measurement procedures (RMPs) was organized by EQA institutes in Italy, the Netherlands, Portugal, UK, and Spain. Results of 17 general chemistry analytes were evaluated across countries and across manufacturers according to performance specifications derived from biological variation (BV). Results: For K, uric acid, glucose, cholesterol and high-density density (HDL) cholesterol, the minimum performance specification was met in all countries and by all manufacturers. For Na, Cl, and Ca, the minimum performance specifications were met by none of the countries and manufacturers. For enzymes, the situation was complicated, as standardization of results of enzymes toward RMPs was still not achieved in 20% of the laboratories and questionable in the remaining 80%. Conclusions: The overall performance of the measurement of 17 general chemistry analytes in European medical laboratories met the minimum performance specifications. In this general picture, there were no significant differences per country and no significant differences per manufacturer. There were major differences between the analytes. There were six analytes for which the minimum quality specifications were not met and manufacturers should improve their performance for these analytes. Standardization of results of enzymes requires ongoing efforts.

Carbohydrate-deficient transferrin (CDT) is used as a biomarker of sustained high alcohol consumption. The currently available measurement procedures for CDT are based on various analytical techniques (HPLC, capillary electrophoresis, nephelometry), some differing in the definition of the analyte and using different reference intervals and cut-off values. The Working Group on Standardization of CDT (WG-CDT), initiated by the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC), has validated an HPLC candidate reference measurement procedure (cRMP) for CDT (% disialotransferrin to total transferrin based on peak areas), demonstrating that it is suitable as a reference measurement procedure (RMP) for CDT. Presented is a detailed description of the cRMP and its calibration. Practical aspects on how to treat genetic variant and so-called di-tri bridge samples are described. Results of method performance characteristics, as demanded by ISO 15189 and ISO 15193, are given, as well as the reference interval and measurement uncertainty and how to deal with that in routine use. The correlation of the cRMP with commercial CDT procedures and the performance of the cRMP in a network of laboratories are also presented. The performance of the CDT cRMP in combination with previously developed commutable calibrators allows for standardization of the currently available commercial measurement procedures for CDT. The cRMP has recently been approved by the IFCC and will be from now on be known as the IFCC-RMP for CDT, while CDT results standardized according to this RMP should be indicated as CDTIFCC.

Background:To provide its participants with an external quality assessment system (EQAS) that can be used to check trueness, the Dutch EQAS organizer, Organization for Quality Assessment of Laboratory Diagnostics (SKML), has innovated its general chemistry scheme over the last decade by introducing fresh frozen commutable samples whose values were assigned by Joint Committee for Traceability in Laboratory Medicine (JCTLM)-listed reference laboratories using reference methods where possible. Here we present some important innovations in our feedback reports that allow participants to judge whether their trueness and imprecision meet predefined analytical performance specifications.Methods:Sigma metrics are used to calculate performance indicators named ‘sigma values’. Tolerance intervals are based on both Total Error allowable (TEa) according to biological variation data and state of the art (SA) in line with the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) Milan consensus.Results:The existing SKML feedback reports that express trueness as the agreement between the regression line through the results of the last 12 months and the values obtained from reference laboratories and calculate imprecision from the residuals of the regression line are now enriched with sigma values calculated from the degree to which the combination of trueness and imprecision are within tolerance limits. The information and its conclusion to a simple two-point scoring system are also graphically represented in addition to the existing difference plot.Conclusions:By adding sigma metrics-based performance evaluation in relation to both TEa and SA tolerance intervals to its EQAS schemes, SKML provides its participants with a powerful and actionable check on accuracy.

BACKGROUND Absolute plasma hepcidin concentrations measured by various procedures differ substantially, complicating interpretation of results and rendering reference intervals method dependent. We investigated the degree of equivalence achievable by harmonization and the identification of a commutable secondary reference material to accomplish this goal. METHODS We applied technical procedures to achieve harmonization developed by the Consortium for Harmonization of Clinical Laboratory Results. Eleven plasma hepcidin measurement procedures (5 mass spectrometry based and 6 immunochemical based) quantified native individual plasma samples (n = 32) and native plasma pools (n = 8) to assess analytical performance and current and achievable equivalence. In addition, 8 types of candidate reference materials (3 concentrations each, n = 24) were assessed for their suitability, most notably in terms of commutability, to serve as secondary reference material. RESULTS Absolute hepcidin values and reproducibility (intrameasurement procedure CVs 2.9%–8.7%) differed substantially between measurement procedures, but all were linear and correlated well. The current equivalence (intermeasurement procedure CV 28.6%) between the methods was mainly attributable to differences in calibration and could thus be improved by harmonization with a common calibrator. Linear regression analysis and standardized residuals showed that a candidate reference material consisting of native lyophilized plasma with cryolyoprotectant was commutable for all measurement procedures. Mathematically simulated harmonization with this calibrator resulted in a maximum achievable equivalence of 7.7%. CONCLUSIONS The secondary reference material identified in this study has the potential to substantially improve equivalence between hepcidin measurement procedures and contributes to the establishment of a traceability chain that will ultimately allow standardization of hepcidin measurement results.

BACKGROUNDProficiency testing (PT), or external quality assessment (EQA), is intended to verify on a recurring basis that laboratory results conform to expectations for the quality required for patient care.CONTENTKey factors for interpreting PT/EQA results are knowledge of the commutability of the samples used and the process used for target value assignment. A commutable PT/EQA sample demonstrates the same numeric relationship between different measurement procedures as that expected for patients' samples. Noncommutable PT/EQA samples frequently have a matrix-related bias of unknown magnitude that limits interpretation of results. PT/EQA results for commutable samples can be used to assess accuracy against a reference measurement procedure or a designated comparison method. In addition, the agreement of the results between different measurement procedures for commutable samples reflects that which would be seen for patients' samples. PT/EQA results for noncommutable samples must be compared to a peer group mean/median of results from participants who use measurement procedures that are expected to have the same or very similar matrix-related bias. Peer group evaluation is used to asses whether a laboratory is using a measurement procedure in conformance to the manufacturer's specifications and/or in conformance to other laboratories using the same technology. A noncommutable PT/EQA sample does not give meaningful information about the relationship of results for patients' samples between different measurement procedures.SUMMARYPT/EQA provides substantial value to the practice of laboratory medicine by assessing the performance of individual laboratories and, when commutable samples are used, the status of standardization or harmonization among different measurement procedures.

In medical laboratories, a metrological basis for quantitation is missing for many tests. This is recognised by the profession and over the last decade the concept of metrological traceability is advocated. However, daily practice is refractable: for many analytes reference measurement procedures are missing and once in place, clinicians obstruct the new units. This wearisome process is described in general terms and illustrated by the specific case of HbA1c. A working group of the scientific division of the IFCC developed a reference system for this key parameter in diabetes management. This system is worldwide accepted as the analytical anchor. However, clinicians objected the new units. A debate of years followed. This urged the international diabetes organisations IDF, EASD and ADA to find a solution to avoid confusion. They came up with a consensus statement, but this compromise—report of HbA1c in three units—was unpractical and not accepted. Finally, decisions were made at a national level: the European Union and Japan will report in the new units, the US in their old national units and an additional unit, the estimated average glucose.

A critical issue in the organisation of Proficiency Testing/External Quality Assessment Schemes is the definition of the criteria against which the performance of individual laboratories should be evaluated. Organisers of EQAS in Occupational and Environmental Laboratory Medicine ( http://www.occupational-environmental-laboratory.com ) collaborate to define common acceptable levels of performance. The aim of this study was to compare the Horwitz function to the Fraser’s approach. Sets of results obtained from the distribution of test materials in the Network schemes (for the measurands: copper, selenium or zinc in serum) were used to calculate Z-scores according to both approaches. Quality specifications derived from both approaches were also compared to the standard deviations obtained. Except for selenium, Horwitz criteria suggests a more stringent evaluation than Fraser criteria, the latter being very stringent as regard the participant analytical variability.

The attraction of the simple biochemical concept combined with a clinical requirement for a long-term marker of glycolic control in diabetes has made hemoglobin A1c (HbA1c) one of the most important assays undertaken in the medical laboratory. The diversity in the biochemistry of glycation, clinical requirements, and management demands has resulted in a broad range of methods being developed since HbA1c was described in the late 1960s. A range of analytic principles are used for the measurement of HbA1c. The charge difference between hemoglobin A0 and HbA1c has been widely utilized to separate these two fractions, most notably found these days in ion-exchange high-performance liquid chromatography systems; the difference in molecular structure (affinity chromatography and immunochemical methods) are becoming widely available. Different results found in different laboratories using a variety of HbA1c analyses resulted in the need for standardization, most notably in the United States, Japan, and Sweden. Designated comparison methods are now located in these three countries, but as they are arbitrarily chosen and have differences in specificity, results of these methods and the reference values and action limits of the methods differ and only harmonized HbA1c in specific geographic areas. A reference measurement system within the concept of metrological traceability is now globally accepted as the only valid analytic anchor. However, there is still discussion over the units to be reported. The consensus statement of the International Federation of Clinical Chemistry (IFCC), the American Diabetes Association, the International Diabetes Federation, and the European Association for the Study of Diabetes suggests reporting HbA1c in IFCC units (mmol/mol), National Glycohemoglobin Standardization Program units (%), and estimated average glucose (either in mg/dl or mmol/liter). The implementation of this consensus statement raised new questions, to be answered in a concerted action of clinicians, biochemists, external quality assessment organizers, patient groups, and manufacturers.

An under-recovery of inorganic mercury added to urine and a wide range of results is observed in quality assessment schemes (EQAS) for trace elements. Further- more, the under-recoveries are inconsistent suggesting features associated with the urine matrix may make the mercury unavailable for measurement. To investigate the instability of mercury in urine the following experiments were set up: (1) a sample of Hg 2? in water with various 'stabilizers' added was sent to UK external quality assessment scheme participants. (2) Urine was collected from volunteers who also completed a 3-day food diary. Hg, Ca, Mg, Se, uric acid, phosphate, creatinine, reducing substances and protein were measured. Inorganic mercury was spiked into the urine, stabilizers were added and the mercury determined following storage. The results con- firmed under-recovery of mercury in association with the urine matrix. Further investigations of how urinary com- ponents affect the measurement of mercury are necessary.

Background: The literature regarding the nonspecificity of applications of the Jaffe (alkaline picrate) reaction for creatinine is generally outdated. We conducted a specificity study to update the nonspecificity information for current Jaffe and enzymatic creatinine assays. Methods: Two serum pools with creatinine concentrations within the pediatric reference interval were spiked with albumin, IgG, unconjugated bilirubin, adult hemoglobin (Hb A), and fetal hemoglobin (Hb F) to produce 1 unspiked and 5 spiked samples per pool. The 35 laboratories participating in the survey used a total of 14 method–analyzer combinations. Measurements were performed in triplicate in a single run in accordance with manufacturer instructions. Absolute differences in creatinine concentration between spiked and unspiked samples were calculated per laboratory. Mixed ANOVA was used to quantify the interferent-related CV component for the Jaffe and enzymatic methods. Results: The interference by bilirubin and Hb A on serum creatinine measurements was Conclusions: Albumin, IgG, and Hb F interfered with Jaffe creatinine assays, leading to inaccuracies in estimated glomerular filtration rates that are clinically important, especially in children and neonates. Because protein error and Hb F interference do not occur with any of the enzymatic methods tested, we conclude that enzymatic creatinine methods are preferred for evaluation of kidney function in pediatric cases.

Background: Trace element external quality assessment schemes monitor laboratory performance and provide a stimulus for improvement in accuracy. However, monitoring of participant performance varies according to the scheme and can lead to conflicting conclusions. Methods: Quality specifications based on biological intra- and interindividual variability were calculated and compared to those currently used by various trace element external quality assessment schemes for plasma or serum copper, zinc, and selenium concentrations. For this purpose, we evaluated results reported by participating laboratories in different schemes, at key concentrations, using z scores. Results: Minimal quality specifications developed from the biological intra- and interindividual variability were, for Cu, ±0.84 μmol/L or 12% of the assigned target concentration, whichever is greater; for Zn, ±1.20 μmol/L or 15% of the assigned target concentration, whichever is greater; and for Se, ±0.072 μmol/L or 12% of the assigned target concentration, whichever is greater. Reported performance of the participating laboratories depended on analyte, concentration, and the selected quality specification. In addition, the most commonly used methods for the determination of Cu, Zn, and Se may give different results. Conclusions: The proposed minimal quality specifications based on biological variation are generally slightly less stringent than those currently in use, although they do not drastically change the performance evaluation in the different schemes. These specifications are a first step in the harmonization of practices among the schemes and remain to be evaluated.

Background: The American Diabetes Association (ADA)/European Association for the Study of Diabetes (EASD)/International Diabetes Federation (IDF)/IFCC Consensus Statement on the worldwide standardization of HbA1c states that “… [HbA1c] results are to be reported world-wide in IFCC units … and derived NGSP units … , using the IFCC-NGSP master equation.” Methods: We describe statistical methods to evaluate and monitor the relationships as expressed in master equations (MEs) between the IFCC Reference Measurement procedure (IFCC-RM) and designated comparison methods (DCMs) [US National Glycohemoglobin Standardization Program (NGSP), Japanese Diabetes Society/Japanese Society for Clinical Chemistry (JDS/JSCC), and Mono-S in Sweden]. We applied these statistics, including uncertainty calculations, to 12 studies in which networks of reference laboratories participated, operating the IFCC-RM and DCMs. Results: For NGSP and Mono-S, slope, intercept, and derived percentage HbA1c at the therapeutic target show compliance with the respective MEs in all 12 studies. For JDS/JSCC, a slight deviation is seen in slope and derived percentage HbA1c in 2 of the 12 studies. Using the MEs, the uncertainty in an assigned value increases from 0.42 mmol/mol HbA1c (IFCC-RM) to 0.47 (NGSP), 0.49 (JDS/JSCC), and 0.51 (Mono-S). Conclusions: We describe sound statistical methods for the investigation of relations between networks of reference laboratories. Application of these statistical methods to the relationship between the IFCC-RM and DCMs in the US, Japan, and Sweden shows that they are suitable for the purpose, and the results support the applicability of the ADA/EASD/IDF/IFCC Consensus Statement on HbA1c measurement.

Background: The IFCC Reference Measurement System for hemoglobin (Hb)A1c (IFCC-RM) has been developed within the framework of metrologic traceability and is embedded in a network of 14 reference laboratories. This paper describes the outcome of 12 intercomparison studies (periodic evaluations to control essential elements of the IFCC-RM).Methods: Each study included: unknown samples (to test individual network laboratories); known samples (controls); recently manufactured calibrators (to check calculated assigned value); stored calibrators (to test stability) and a calibration-set (to calibrate the IFCC-RM). The unknown samples are measured by use of the IFCC-RM and the designated comparison methods [DCMs; the National Glycohemoglobin Standardization Program (NGSP) in the US, Japanese Diabetes Society/Japanese Society for Clinical Chemistry (JDS/JSCC) in Japan, and Mono-S in Sweden] are used to investigate the stability of the Master Equation (ME), the relationship between IFCC-RM and DCMs.Results: A total of 105 IFCC-RM data sets were evaluated: 95 were approved, 5 were not, and for 5 no data were submitted. Trend analysis of the MEs, expressed as change in percentage HbA1c per year, revealed 0.000% (NGSP, not significant), −0.030%, (JDS/JSCC; significant) and −0.016% (Mono-S; not significant). Evaluation of long-term performance revealed no systematic change over time; 2 laboratories showed significant bias, 1 poor reproducibility. The mean HbA1c determined by laboratories performing mass spectrometry (MS) was the same as the mean determined by laboratories using capillary electrophoresis (CE), but the reproducibility at laboratories using CE was better. One batch of new calibrators was not approved. All stored calibrators were stable.Conclusion: A sound reference system is in place to ensure continuity and stability of the analytical anchor for HbA1c.

Carbohydrate-deficient transferrin (CDT) is a glycoform profile of serum transferrin that increases in response to sustained high alcohol intake and over the last decades has become an important alcohol biomarker with clinical and forensic applications. However, the wide range of CDT measurement procedures has resulted in lack of uniform results and reference limits, and hampered comparison of results. In 2005, the IFCC therefore founded a special working group (WG) aiming for standardisation of CDT measurement. This review summarises the history of CDT and the actions taken by the WG-CDT. Initial steps included the definition of the measurand (serum disialotransferrin to total transferrin fraction expressed in %), and the determination of a well-defined anion-exchange HPLC procedure as the candidate reference measurement procedure (cRMP). Subsequent achievements were the establishment of a network of reference laboratories to perform the cRMP, setting a reference interval, and development of a reference material based on human serum for which the laboratory network assign values. Using a set of reference materials for calibration allowed for achieving equivalence of results of all present CDT measurement procedures. The final steps of the WG-CDT have been a full validation of the cRMP to make it an IFCC approved RMP, and providing guidance for international standardisation of all CDT measurement procedures.

Carbohydrate-deficient transferrin (CDT) is a glycoform profile of serum transferrin that increases in response to sustained high alcohol intake and over the last decades has become an important alcohol biomarker with clinical and forensic applications. However, the wide range of CDT measurement procedures has resulted in lack of uniform results and reference limits, and hampered comparison of results. In 2005, the IFCC therefore founded a special working group (WG) aiming for standardisation of CDT measurement. This review summarises the history of CDT and the actions taken by the WG-CDT. Initial steps included the definition of the measurand (serum disialotransferrin to total transferrin fraction expressed in %), and the determination of a well-defined anion-exchange HPLC procedure as the candidate reference measurement procedure (cRMP). Subsequent achievements were the establishment of a network of reference laboratories to perform the cRMP, setting a reference interval, and development of a reference material based on human serum for which the laboratory network assign values. Using a set of reference materials for calibration allowed for achieving equivalence of results of all present CDT measurement procedures. The final steps of the WG-CDT have been a full validation of the cRMP to make it an IFCC approved RMP, and providing guidance for international standardisation of all CDT measurement procedures.

Background Hemoglobin C, D Punjab, E or S trait can interfere with hemoglobin A1c (HbA1c) results. We assessed whether they affect results obtained with 12 current assay methods. Methods Hemoglobin AA (HbAA), HbAC, HbAD Punjab, HbAE and HbAS samples were analyzed on one enzymatic, nine ion-exchange HPLC and two Capillary Electrophoresis methods. Trinity ultra2 boronate affinity HPLC was the comparative method. An overall test of coincidence of least-squared linear regression lines was performed to determine if HbA1c results were statistically significantly different from those of HbAA samples. Clinically significant interference was defined as > 7% difference from HbAA at 6 or 9% HbA1c compared to ultra2 using Deming regression. Results All methods showed statistically significant effects for one or more variants. Clinically significant effects were observed for the Tosoh G8 variant mode and GX (all variants), GX V1.22 (all but HbAE) and G11 variant mode (HbAC). All other methods (Abbott Architect c Enzymatic, Bio-Rad D-100, Variant II NU and Variant II Turbo 2.0, Menarini HA-8180T thalassemia mode and HA-8180V variant mode, Sebia Capillarys 2 and Capillarys 3) showed no clinically significant differences. Conclusions Several methods showed clinically significant interference with HbA1c results from one or more variants which could adversely affect patient care.

Background The determination of glycated hemoglobin is a key indicator for the management of diabetic patients. A reference measurement system for its determination is available and IVD manufacturers should have aligned their assay to this system. Methods Two fresh blood samples were distributed by courier to 206 Italian laboratories asking for the determination of their HbA 1c concentration. Target HbA 1c values were assigned by the IFCC reference measurement procedure. Results From 193 laboratories using analytical systems from five manufacturers (Bio-Rad Laboratories, A. Menarini Diagnostics, Roche Diagnostics, Sebia and Tosoh), we obtained a global variability of 5.3% (in terms of CV) and of 3.8% at an HbA 1c value of 37.4 mmol/mol (sample 1) and 62.0 mmol/mol (sample 2), respectively. With a goal for the allowable total error (TE) of 6.0%, 70% and 77% of the participants met this criterion for samples 1 and 2, respectively. Inter-laboratory CVs, were between 3.3 and 5.0% and between 2.2 and 3.7% for samples 1 and 2, respectively. Tosoh users registered the smallest inter-laboratory CV in sample 1, and Sebia's in sample 2. With regard to trueness, all methods had a mean bias of ≤ 2.8% with respect to the target values, with the exception of Tosoh (bias of + 6.1 and + 5.8%, for samples 1 and 2, respectively). Conclusion These results are in good agreement with those obtained by the CAP 2014 GH2-A survey, suggesting then that still there is an urgent need for improving a significant part of the methods currently used to measure HbA 1c .

Working group (WG) discussions on proficiency testing and external quality assessment held at the Eurachem workshop, Portorož, Slovenia 26–27 Sept 2005 are summarised. The discussions focused on performance criteria (WG 1), different aspects of accreditation (WGs 2–3), the revised international harmonised protocol (WG 4), pre- and post-analytical schemes (WG 5), Internet applications (WG 6), experience from the CoEPT project (WG 7), and future aspects (WG 8). Current status, problems and future directions were identified. The WG contained a mix of participants with different expertise. This was done to promote cross-fertilisation of ideas between sectors. The WG issues reflected the content of the keynote lectures and some issues were covered from different perspectives by more than one WG.

Most people in any community come into contact with chemicals that are potentially harmful to their health. Some elements are essential to health and inadequate amounts in food may also lead to ill health. Measurement of chemicals in blood, urine or other specimens is a fundamental feature of studies undertaken in the field of Occupational and Environmental Laboratory Medicine (OELM). Results are used to assess the risk for either overexposure or deficiency of essential nutrients. External Quality Assessment Schemes (EQAS) aid laboratories to achieve accurate and consistent data and 11 organisers of EQAS in Europe and North America are working to improve the effectiveness of their activities. The aims of the Network of EQAS Organisers in OELM are to stimulate improvements in analytical results, establish equivalence of assessment among Schemes, collaborate to enhance the practice of EQA including whenever possible to warrant traceability of EQAS to primary standards.

Quality specifications (QS) are proposed for lead in blood and for aluminium, copper, selenium and zinc in serum as part of the aim to set standards of performance for laboratories so that results can be demonstrated to be fit for the purpose to which they are applied. The QS were established taking account of the analytical state-of-the-art, physiological variations in the concentrations of the analyte and the clinical purpose for which the assay is to be used. A procedure was devised that uses these QS to give equivalence of assessment among external quality assessment schemes (EQAS), thus avoiding conflicting information which has been demonstrated in the past. Advantages of this procedure are: to provide direct comparison of performance of laboratories taking part in different schemes, to provide equivalence of assessment of laboratory performance necessary to establish mutual recognition agreements, and to demonstrate the fitness for purpose of results from participants.

Within the last decade, the IFCC HbA1c standardization network has established the metrologically highest reference measurement procedure for HbA1c testing. Based on this procedure, reference calibrators are produced which in turn provide the starting point for the standardization of the manufactures routine HbA1c assays. According to the IVD directive, the uncertainty of the reference calibrators must be calculated and reported together with their assigned values. Within this article, we elaborate the uncertainty calculation according to GUM (guide to the expression of uncertainty in measurement) in detail. Finally, the results are validated by a simulation study.

Background Haemoglobin (Hb) variants are well-known factors interfering with accurate HbA1c testing. This report describes two novel Hb variants leading to inappropriate quantification of HbA1c by ion-exchange chromatography. Methods Glycated forms of novel Hb variants were recognised in the blood of two patients with diabetes mellitus screened by HbA1c ion-exchange chromatography. Dedicated high-resolution cation-exchange chromatography and subsequent DNA sequencing revealed the exact nature of the variants. Other common techniques for quantifying HbA1c were applied on both samples and haematological parameters were determined to judge possible pathology associated with the novel Hb variants. Results A fraction of 15% of abnormal Hb was observed in a 37-year-old female. DNA sequencing revealed a heterozygous mutation in the α1-globin gene, resulting in a leucine-to-phenylalanine amino-acid substitution (HBA1: c.301C>T, p.Leu101Phe). We named this variant Hb Weesp. The other novel variant, Hb Haelen, presented as a 40% fraction in a 63-year-old male and resulted from a heterozygous amino acid substitution in the β-globin gene (HBB: c.335T>C, p.Val112Gly). The presence of both Hb variants resulted in aberrant separation of the Hb components, leading to an inadequate quantification of HbA1c. Conclusions Close examination of HbA1c chromatograms revealed two novel, clinically silent Hb variants that interfere with HbA1c quantification. Healthcare providers need to be aware of the potential of such Hb variants when interpreting HbA1c results.

Background: The different scoring methods used by eight European External Quality Assessment Schemes (EQASs) for occupational and environmental laboratory medicine were compared to develop suitable quality specifications as a step toward harmonization. Methods: Real results for blood lead and serum aluminum assays, reported by participants in Italian and United Kingdom EQASs, were evaluated according to individual scheme scoring criteria. The same results were then used to produce z scores using scheme-based between-laboratory SDs as the estimate of variability to determine whether simple performance-derived quality specifications produced better agreement among schemes. Results: The schemes gave conflicting assessments of participants’ performance, and participants judged to be successful by one scheme could be defined as performing inadequately by another. An approach proposed by Kenny et al. (Scand J Clin Lab Invest 1999;59:585), which uses clinical inputs to set targets for analytical imprecision, bias, and total error allowable, was then used to elaborate quality specifications. Conclusions: We suggest that the CLIA ′88 recommendations for blood lead (± 40 μg/L or ± 10% of the target concentration, whichever is the greater) could be used as a quality specification, although a revision to ± 30 μg/L or ± 10% is recommended. For serum aluminum, a suitable quality specification of ± 5 μg/L or ± 20% of the target concentration, whichever is the greater, is suggested. These specifications may be used to compare laboratory performance across schemes.