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Impaired beta-cell function is a recognized cornerstone of diabetes pathophysiology. Estimates of insulin secretory capacity are useful to inform clinical practice, helping to classify types of diabetes, complication risk stratification and to guide treatment decisions. Because C-peptide secretion mirrors beta-cell function, it has emerged as a valuable clinical biomarker, mainly in autoimmune diabetes and especially in adult-onset diabetes. Nonetheless, the lack of robust evidence about the clinical utility of C-peptide measurement in type 2 diabetes, where insulin resistance is a major confounder, limits its use in such cases. Furthermore, problems remain in the standardization of the assay for C-peptide, raising concerns about comparability of measurements between different laboratories. To approach the heterogeneity and complexity of diabetes, reliable, simple and inexpensive clinical markers are required that can inform clinicians about probable pathophysiology and disease progression, and so enable personalization of management and therapy. This review summarizes the current evidence base about the potential value of C-peptide in the management of the two most prevalent forms of diabetes (type 2 diabetes and autoimmune diabetes) to address how its measurement may assist daily clinical practice and to highlight current limitations and areas of uncertainties to be covered by future research.

The standardization of C-peptide assays is highly desirable objective. Our groups have employed the use of a Certified Reference Material (CRM) to calibrate their respective measurement procedures and comparison studies have demonstrated good agreement between the two laboratories [Figure]. Although it was the original choice, The National Metrology Institute of Japan (NMIJ) CRM has not always been available. However, a new material from Cerilliant (C-161-0.1ML) proved equally well defined. Both materials include known amounts of pure C-peptide and small amounts of deamidated and pyroglutamated forms (Cerilliant Lot# FN0422195.6% modified; NMIJ CRM 6901-b, Lot# 058 1.9% modified) . The C-peptide CRMs from Cerilliant and from NMIJ behave identically when the mass concentration of the unmodified C-peptide is used to assign calibrator concentrations. To avoid potential bias, we conclude that the mass concentration of unmodified C-peptide (not the mass concentration of total C-peptide) in CRM should be used when making calibrators for mass spectrometry C-peptide assays to achieve comparable patient results. Variation in the relative amount of modified C-peptide is an obstacle to standardization, especially when comparing mass spectrometry-based assays with immunoassays, which use total C-peptide for calibration. Disclosure Z.Wu: Employee; Quest Diagnostics. K.Kabytaev: None. J.Mu: None. S.Connolly: None. M.J.Mcphaul: Employee; Quest Diagnostics. R.R.Little: None. Funding NIH/NIDDK (1UC4DK096587-01)

BACKGROUND Measurement of hemoglobin A1c (HbA1c) in the blood is integral to and essential for the treatment of patients with diabetes mellitus. HbA1c reflects the mean blood glucose concentration over the preceding 8 to 12 weeks. Although the clinical value of HbA1c was initially limited by large differences in results among various methods, the investment of considerable effort to implement standardization has brought about a marked improvement in analysis. CONTENT The focus of this review is on the substantial progress that has been achieved in enhancing the accuracy and, therefore, the clinical value of HbA1c assays. SUMMARY The interactions between the National Glycohemoglobin Standardization Program and manufacturers of HbA1c methods have been instrumental in standardizing HbA1c. Proficiency testing using whole blood has allowed accuracy-based assessment of methods in individual clinical laboratories that has made an important contribution to improving the HbA1c measurement in patient samples. These initiatives, supported by the efforts of the IFCC network, have led to a continuing enhancement of HbA1c methods. Many of the factors that previously influenced HbA1c results independently of blood glucose have been eliminated from most modern methods. These include carbamylation, labile intermediates, and common hemoglobin variants. Nevertheless, some factors (e.g., race and aging) may alter HbA1c interpretation, but whether these differences have clinical implications remains contentious. HbA1c has a fundamental role in the diagnosis and management of diabetes. Ongoing improvements in HbA1c measurement and quality will further enhance the clinical value of this analyte.

BACKGROUND AND OBJECTIVES: Among people with diabetes mellitus, CKD may promote hypoglycemia through altered clearance of glucose-lowering medications, decreased kidney gluconeogenesis, and blunted counter-regulatory response. We conducted a prospective observational study of hypoglycemia among 105 individuals with type 2 diabetes treated with insulin or a sulfonylurea using continuous glucose monitors. DESIGN, SETTING, PARTICIPANTS & MEASUREMENTS: We enrolled 81 participants with CKD, defined as eGFR

No point of care HbA1c (A1c) assays are CLIA waived for use in diagnosing diabetes. The accuracy of the Abbott Afinion HbA1c Dx (Afinion) was evaluated for this purpose. Operators with no laboratory training (N=21) tested fingerstick (FS) and venous (V) whole blood samples from subjects at 7 CLIA waived sites with 2 Afinion analyzer models (AS100 and Afinion 2). Operators self-trained on use of the Afinion using only materials that are provided when the test is purchased. A portion of each subject’s V sample was tested with a recognized comparative method (CM) at an NGSP Secondary Reference Laboratory (SRL). Consistent with FDA requirements for total error of A1c test systems, the percentage of Afinion results within an Allowable Total Error (ATE) zone of ±6% of the CM result was calculated, as well as the bias at 6.5% A1c. A total of 1,229 subjects with A1c values spanning the Afinion assay measuring range were enrolled. For the Afinion 2, 95.04% (95% lower confidence limit, LCL: 93.33%) of FS and 94.86% (95% LCL: 93.12%) of V results were within the ATE zone. For the AS100, 94.22% (95% LCL: 92.38%) and 93.36% (95% LCL: 91.41%) of Afinion results were within the ATE zone for FS and V samples, respectively. The bias at 6.5% A1c for the Afinion 2 was -0.13% (-0.008% A1c units) for FS and 0.01% (0.000% A1c units) for V samples. For the AS100, the bias was 0.62% (0.040% A1c units) and 1.13% (0.073% A1c units) for FS and V samples, respectively. No operator effects and no differences between the Afinion and CM results that could potentially impact clinical decision making were observed in this study. In subjects with unreported hemoglobin variants (detected by CM), 16/16 FS and 15/16 V Afinion results were within the ATE zone when compared to a second NGSP certified method at the same SRL. These data support the use of Afinion in CLIA waived settings to diagnose diabetes. Disclosure M. Clendenin: Employee; Self; Abbott. A. J. Nation: None. R. C. San george: Other Relationship; Self; Abbott. K. Kupfer: Employee; Self; Abbott. K. S. Fortner: Employee; Self; Abbott. R. R. Little: None. T. S. Bailey: Consultant; Self; Abbott Diabetes, LifeScan, Novo Nordisk, Sanofi, Research Support; Self; Abbott, Abbott Diabetes, Biolinq, Capillary Biomedical, Inc., Dexcom, Inc., Eli Lilly and Company, Kowa Research Institute, Inc., Lexicon Pharmaceuticals, Inc., Livongo, Medtronic, Medtrum Technologies, Novo Nordisk, REMD Biotherapeutics, Sanofi, Sanvita, Viacyte, Inc., vTv Therapeutics, Zealand Pharma A/S, Speaker’s Bureau; Self; BD, Medtronic, Sanofi. K. N. Castorino: Consultant; Self; Dexcom, Inc., Research Support; Self; Abbott Diabetes, Abbott Laboratories, Dexcom, Inc., Drawbridge Health, Inc., Lilly Diabetes, Medtronic, Novo Nordisk Inc. D. S. Denham: None. E. Kerwin: Consultant; Self; Amphastar, AstraZeneca, Connect Biopharma, GlaxoSmithKline plc., Mylan N. V., Novartis Pharmaceuticals Corporation, Sunovion Pharmaceuticals Inc., Theravance Biopharma, Speaker’s Bureau; Self; Chiesi USA, Inc. M. Mickiewicz: None.

Background Glycated albumin is considered an alternative glycemic indicator in certain situations where HbA1c does not accurately reflect glycemic status. These patient cases are usually associated with decreased erythrocyte lifespan, gestational diabetes, or end-stage renal disease. The aim of our study was to develop an assay for absolute quantitation of glycated albumin based on isotope dilution liquid chromatography-mass spectrometry. Methods The plasma samples were reduced/alkylated, spiked with isotope-labeled standards RQIKKQTALV(D8)E and RQIKK(fructosyl)QTALV(D8)E and enzymatically digested by Glu-C. The samples were analyzed on an LC–MS system. Two MRM transitions (M3+ → (b9-3H2O)2+ and M3+ → (b10-3H2O)2+ or M3+ → b92+ and M3+ → b102+) were used for each peptide, then the percentage of glycation (MS GA%) was calculated. Results The comparison study demonstrated a good linear correlation between our LC–MS/MS and Lucica method with r2 = 0.95. The intra-day CV for the low HbA1c sample was 2.2%, while CV for the high HbA1c sample was 0.64%. Inter-day CV for low HbA1c sample was 5.6%, while the CV for the high HbA1c sample was 5.7%. We found the LLOQ to be 0.12 nmol/ml for the non-glycated and glycated peptide. No interference from hemoglobin was observed up to 500 mg/dL concentration. Conclusions This is the first implementation of isotope dilution LC–MS assay for glycated albumin with simultaneously quantitation of glycated and non-glycated peptides. The method includes a simple sample preparation and has demonstrated a good analytical performance.

Background Hemoglobin C, D Punjab, E or S trait can interfere with hemoglobin A1c (HbA1c) results. We assessed whether they affect results obtained with 15 current assay methods. Methods Hemoglobin AA (HbAA), HbAC, HbAD Punjab, HbAE and HbAS samples were analyzed on 2 enzymatic, 4 ion-exchange HPLC and 9 immunoassay methods. Trinity Premier Hb9210 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 >6% difference from HbAA at 6 or 9% HbA1c compared to Premier Hb9210 using Deming regression. Results All methods showed statistically significant effects for one or more variants. Clinically significant effects were observed for the Tosoh G11 variant mode (HbAD), Roche b 101 (HbAC and HbAE) and Siemens DCA Vantage (HbAE and HbAS). All other methods (Beckman Coulter B93009 and B00389 on DxC700AU, and Unicel DxC, Ortho Clinical Vitros 5.1, Roche cobas c 513, Siemens Dimension RxL and Vista, and Enzymatic on Advia and Atellica, Tosoh G8 5.24 and 5.28, and GX) showed no clinically significant differences. Conclusions A few methods showed interference from one or more variants. Laboratories need to be aware of potential HbA1c assay interferences.

Objective: In chronic kidney disease (CKD), glycated albumin and fructosamine have been postulated to be better biomarkers of glycemic control than HbA1c. We evaluated accuracy, variability, and covariate bias of three biomarkers (HbA1c, glycated albumin, and fructosamine) compared with continuous glucose monitoring (CGM)-derived measurement of glycemia across estimated glomerular filtration rate (eGFR) in type 2 diabetes. Research Design and Methods: Prospective cohort study of 104 participants with type 2 diabetes, 80 with eGFR 2 (not treated with dialysis) and 24 frequency-matched controls with eGFR ≥60 mL/min/1.73m2. Participants wore a blinded CGM for 2 six-day periods separated by two weeks, with blood and urine collected at the end of each CGM period. HbA1c, glycated albumin and fructosamine were measured by HPLC, enzymatic, and colorimetric nitroblue tetrozolium methods, respectively. Results: Within-person biomarker values were strongly correlated between the two CGM periods (r=0.92-0.95), although no marker fully captured the within-person variability of mean CGM glucose. All markers were similarly correlated with mean CGM glucose (r = 0.71-77). Compared with mean CGM glucose, glycated albumin and fructosamine were significantly biased by age, BMI, serum iron concentration, transferrin saturation, and albuminuria; HbA1c was under-estimated in those with albuminuria. Conclusions: Glycated albumin and fructosamine were not less variable than HbA1c at a given mean CGM glucose level, with several additional sources of bias. These results support measuring HbA1c to monitor trends in glycemia among patients with eGFR 2. Direct measurements of glucose are necessary to capture short-term variability.

OBJECTIVE In chronic kidney disease, glycated albumin and fructosamine have been postulated to be better biomarkers of glycemic control than HbA1c. We evaluated the accuracy, variability, and covariate bias of three biomarkers (HbA1c, glycated albumin, and fructosamine) compared with continuous glucose monitoring (CGM)–derived measurement of glycemia across estimated glomerular filtration rate (eGFR) in type 2 diabetes. RESEARCH DESIGN AND METHODS A prospective cohort study was conducted of 104 participants with type 2 diabetes, 80 with eGFR RESULTS Within-person biomarker values were strongly correlated between the two CGM periods (r = 0.92–0.95), although no marker fully captured the within-person variability of mean CGM glucose. All markers were similarly correlated with mean CGM glucose (r = 0.71–77). Compared with mean CGM glucose, glycated albumin and fructosamine were significantly biased by age, BMI, serum iron concentration, transferrin saturation, and albuminuria; HbA1c was underestimated in those with albuminuria. CONCLUSIONS Glycated albumin and fructosamine were not less variable than HbA1c at a given mean CGM glucose level, with several additional sources of bias. These results support measuring HbA1c to monitor trends in glycemia among patients with eGFR

Background Unrecognized hemoglobinopathies can lead to measured hemoglobin A1c (Hb A1c) concentrations that are erroneous or misleading. We determined the effects of rare hemoglobin variants on capillary electrophoresis (CE) and HPLC methods for measurement of Hb A1c. Methods We prospectively investigated samples in which Hb A1c was measured by CE during a 14-month period. For samples in which the electropherograms suggested the presence of rare hemoglobinopathies, hemoglobin variants were identified by molecular analysis or by comparison with electropherograms of known variants. When sample volume permitted, Hb A1c was measured by 2 HPLC measurement procedures and by boronate affinity HPLC. Results Hb A1c was measured by CE in 33,859 samples from 26,850 patients. 15 patients (0.06%) were identified as having rare hemoglobinopathies: Hbs A2 prime, Agenogi, Fannin-Lubbock I, G Philadelphia, G San Jose, J Baltimore, La Desirade, N Baltimore, Nouakchott, and Roanne. Among 6 of these samples tested by 2 ion-exchange HPLC methods, the rare Hb was detected by both HPLC methods in only one sample, and none were detected by boronate affinity HPLC. The mean of the Hb A1c results of 2 HPLC methods differed from the result of the CE method by 0.7–2.2% Hb A1c in samples with variant hemoglobins versus Conclusion Measurement procedures differ in the ability to detect the presence of rare Hb variants and to quantify Hb A1c in patients who harbor such variants.

Background: Point-of-care (POC) hemoglobin A1c (HbA1c) testing has advantages over laboratory testing, but some questions have remained regarding the accuracy and precision of these methods. The accuracy and the precision of the POC Afinion™ HbA1c Dx test were investigated. Methods: Samples spanning the assay range were collected from prospectively enrolled subjects at three clinical sites. The accuracy of the POC test using fingerstick and venous whole blood samples was estimated via correlation and bias with respect to values obtained by an NGSP secondary reference laboratory (SRL). The precision of the POC test using fingerstick samples was estimated from duplicate results by calculating the coefficient of variation (CV) and standard deviation (SD), and separated into its components using analysis of variance (ANOVA). The precision of the POC test using venous blood was evaluated from samples run in four replicates on each of three test cartridge lots, twice per day for 10 consecutive days. The SD and CV by study site and overall were calculated. Results: Across the assay range, POC test results from fingerstick and venous whole blood samples were highly correlated with results from the NGSP SRL ( r = .99). The mean bias was −0.021% HbA1c (−0.346% relative) using fingerstick samples and −0.005% HbA1c (−0.093% relative) using venous samples. Imprecision ranged from 0.62% to 1.93% CV for fingerstick samples and 1.11% to 1.69% CV for venous samples. Conclusions: The results indicate that the POC test evaluated here is accurate and precise using both fingerstick and venous whole blood.

IA sensitively predict future T1D, but onset often occurs many years after seroconversion. Early diagnosis results in less DKA and milder initial disease, especially in young children. Using the international TEDDY cohort, we asked if quarterly HbA1c testing could predict T1D among pre-pubertal subjects with ≥1 persistent IA (GADA, IA2A, IAA). Mean(SD) age at seroconversion and T1D onset was 43(29) and 73(22) months respectively. Of 8,504 HLA high risk children, 456 had persistent confirmed IA, had undergone at least 3 quarterly HbA1c tests in the prior 12 months, and were not on diabetes drugs or diets. Of these, 104 progressed to T1D and 352 did not. Subjects were split into training (292 total, 62 progressors) and test (164 total, 40 progressors) datasets with similar characteristics. The optimal maximum HbA1c cutpoint within 1 year pre-onset to predict T1D, by ROC analysis, was similar in training and test datasets (p=0.66). For both, HbA1c ≥5.6% gave the best Youden index. Other factors significant for T1D risk in the training dataset included age at HbA1c test, month of HbA1c test, continent and IA2A titer, but not gender, family history, HLA type, seroconversion age, IAA titer nor T1D-related SNP genotypes. Adjusted for significant factors, the optimal HbA1c cutpoint of ≥5.6% for quarterly testing was 91% sensitive, 91% specific, 73% PPV and 98% NPV to predict T1D within 1 year in children with HLA and IA risk. The final predictive model fit both training and test data similarly (p=0.28). Median(SD) time from first HbA1c ≥5.6% to diagnosis was 8.6(4.5) months, enabling monitoring and education for earlier treatment. Quarterly HbA1c surveillance is cost-effective and clinically accessible. A hierarchical plan for pediatric T1D prediction is proposed comprising initial genetic screening, then IA surveillance of those at genetic risk, then HbA1c surveillance of those with IA, and finally close glycemic surveillance of those with HbA1c ≥5.6% to ascertain metabolic onset. Disclosure M. Killian: None. K. Vehik: None. R.R. Little: None. H. Elding Larsson: None. M.J. Haller: None. M. Rewers: None. J. She: None. J. Toppari: None. B. Akolkar: None. J. Krischer: None. W. Hagopian: None.

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.

A liquid chromatography with mass spectrometry on-line platform that includes the orthogonal techniques of ion exchange and reversed phase chromatography is applied for C-peptide analysis. Additional improvement is achieved by the subsequent application of cation- and anion-exchange purification steps that allow for isolating components that have their isoelectric points in a narrow pH range before final reversed-phase mass spectrometry analysis. The utility of this approach for isolating fractions in the desired "pI window" for profiling complex mixtures is discussed.

Objective: This study was designed to develop a dental-office-friendly diabetes self-screening tool for diabetes mellitus (DM) and prediabetes (PreDM). Methods: Consecutive dental patients, aged 18 years or older, without history of DM or PreDM, completed a 14-question questionnaire without assistance. They subsequently underwent onsite finger-sticks for capillary blood collection for glycohemoglobin (A1c) measurement. Results: Of the total 500 patients who completed the study, 302 were women (60.4%) and 198 were men (39.6%), with a collective mean age of 47.8 (±16.8) years old. The prevalence of PreDM and DM was 19.2% and 1.2%, respectively. Predictors of PreDM or DM included age, >10% above ideal body weight, waist size above 40” for men or 35” for women, reported hypertension, reported abnormal lipids, tingling of hands or feet, and visual symptoms or conditions (blurring, cataracts, glaucoma). Conclusions: This study introduces a newly developed, user-friendly, PreDM and DM self-screening tool, abbreviated as DiDDO (Diabetes detection in the dental office). This screening tool requires no body weighing or BMI calculation (undesirable by dentists) nor laboratory tests or blood pressure measurement, allowing dentists to identify patients at moderate and high risk for DM/PreDM, and perform (or refer for) diagnostic A1c testing. This dental-office-friendly self-screening tool is proposed for validation in other dental populations.

Background: Monitoring of HbA1c is the standard of care to assess diabetes control. In Trinidad & Tobago (T&T) there are no existing data on the quality of HbA1c measurement. Our study examined the precision and accuracy of HbA1c testing in T&T. Methods: Sets of 10 samples containing blinded duplicates were shipped to laboratories in T&T. This exercise was repeated 6 months later. Precision and accuracy were estimated for each laboratory/method. Results: T&T methods included immunoassay, capillary electrophoresis, and boronate affinity binding. Most, but not all, laboratories demonstrated acceptable precision and accuracy. Conclusions: Continuous oversight of HbA1c testing (eg, through proficiency testing) in T&T is recommended. These results highlight the lack of oversight of HbA1c testing in some developing countries.

Background Hemoglobin A1c (HbA1c) is used to monitor long-term glycemic control in individuals with diabetes, guide therapy, predict the risk of microvascular complications, and more recently to diagnose diabetes. An automated liquid-flow capillary electrophoresis method was recently developed to measure HbA1c using the Capillarys 2 Flex Piercing instrument. Methods Analytical evaluation was performed at 2 clinical centers. A clinical analysis was conducted in 109 African-born individuals, 24% of whom have variant hemoglobin (HbAS or HbAC). Abnormal glucose tolerance (which includes both diabetes and prediabetes) was defined as 2 h glucose of ≥ 140 mg/dl (7.8 mmol/l) during an oral glucose tolerance test. Results Interlaboratory CVs were ≤ 2.1%. The method showed satisfactory correlation with 2 other analyzers that measure HbA1c by high-performance liquid chromatography. Neither labile HbA1c, carbamylated hemoglobin, uremia, bilirubin nor common hemoglobin variants (HbC/HbS/HbE) interfered. Forty-five individuals (41%) had abnormal glucose tolerance. The sensitivity of HbA1c for diagnosing abnormal glucose tolerance was 38%, 36% and 42% for total, normal and variant hemoglobin groups, respectively. Conclusions The analytical performance of HbA1c on the Capillarys 2 is suitable for clinical application. Variant hemoglobin in Africans did not interfere with the detection of abnormal glucose tolerance by HbA1c measured on the Capillarys 2.

Unrecognized hemoglobinopathies can lead to measured hemoglobin AWe prospectively investigated samples in which Hb AHb AMeasurement procedures differ in the ability to detect the presence of rare Hb variants and to quantify Hb A

BACKGROUND Assessment of endogenous insulin secretion by measuring C-peptide concentrations is widely accepted. Recent studies have shown that preservation of even small amounts of endogenous C-peptide production in patients with type 1 diabetes reduces risks for diabetic complications. Harmonization of C-peptide results will facilitate comparison of data from different research studies and later among clinical laboratory results at different sites using different assay methods. CONTENT This review provides an overview of the general process of harmonization and standardization and the challenges encountered with implementing a reference measurement system for C-peptide. SUMMARY Efforts to harmonize C-peptide results are described, including those by the National Institute of Diabetes and Digestive and Kidney Diseases–led C-peptide Standardization Committee in the US, activities in Japan, efforts by the National Institute for Biological Standards and Control in the UK, as well as activities led by the Bureau International des Poids et Mesures and the National Metrology Institute in China. A traceability scheme is proposed along with the next steps for implementation. Suggestions are made for better collaboration to optimize the harmonization process for other measurands.

Isotope Dilution Analysis (IDA) allows quantitation of elements and different compounds in complex mixtures. The quantitation is based on a known amount of reference material (Internal Standard, IS) added to a sample that makes the result critically dependent on the value assigned to the standard. In the case of peptides, IS concentration is determined by nitrogen and amino acid analysis while purity is normally assessed by methods such as chromatography or electrophoresis that might not be able to detect many possible amino acid modifications, either naturally occurring or chemically induced. Microheterogeneity of the IS, if it isn’t accounted for when assigning a reference value to the standard, results in highly overestimated values in target analyte quantitation. In this viewpoint article we illustrate the problem of internal standard microheterogeneity by analyzing synthetic human C-peptide labeled analogues.

Glycated hemoglobin (GHb), reported as HbA1c, is used as marker of long-term glycemia for diabetic patients. HbA1c results from boronate affinity methods are generally considered to be unaffected by most hemoglobin variants; this assumes comparable glycation of variant and non-variant (HbAA) hemoglobins. In this report, glycation of HbA beta chain (βA) and HbS beta chain (βS) for the most common Hb variant trait (HbAS) are examined.We analyzed 41 blood samples from subjects with HbAS, both with and without diabetes. Using LC-MS, ratios of glycated HbS to glycated HbA were determined by comparison of areas under the curves from extracted ion chromatograms.Glycation of βS chains was significantly higher (p0.001) than βA chains; this difference was consistent across subjects. Total (α+β) glycated HbAS was theoretically estimated to be ~5% higher than glycated HbAA.This novel mass-spectrometric approach described allows for relative quantification of glycated forms of βS and βA. Although βS glycation was significantly higher than that of βA, the difference in total glycation of HbAS versus HbAA was smaller and unlikely to impact clinical interpretation of boronate affinity HbA1c results. These data support the continued use of boronate affinity to measure HbA1c in patients with HbAS.

BACKGROUND: Hemoglobin A1c (HbA1c) is an important index of average glycemia in patients with diabetes mellitus that is widely used in clinical trials and large-scale epidemiological studies. Previous studies have shown that adverse sample storage conditions can cause erroneous HbA1c results. We examined the effect of storage at different temperatures with five current HbA1c methods: Tosoh G7 and G8 (Tosoh Bioscience, Inc., South San Francisco, CA) and Bio-Rad Variant™ II (Bio-Rad Laboratories, Hercules, CA) (all ion-exchange high-performance liquid chromatography); Siemens DCA 2000+ (Siemens Healthcare Diagnostics, Deerfield, IL) (immunoassay); and Trinity Biotech (Kansas City, MO) ultra(2) (boronate-affinity high-performance liquid chromatography). METHODS: Five whole blood specimens with different HbA1c levels were analyzed by each assay method on Day 0 and then divided into aliquots that were stored at six different temperatures (−70°C, −20°C, 4°C, room temperature, 30°C, and 37°C) for analyses on subsequent days out to Day 84. Acceptance limits were defined as within ±3 SD of all −70°C results or ±0.2% HbA1c, whichever was wider, for each sample. Stability was considered acceptable for a given temperature only if results for all five specimens were acceptable on that day. RESULTS: The DCA 2000+ demonstrated the best stability at −20°C and room temperature, whereas the ultra(2) showed the best stability with specimens stored at 4°C. No methods demonstrated stability at 30°C or 37°C for more than 3 days. CONCLUSIONS: Exposure of specimens to high temperatures should be avoided regardless of assay methodology. For the ion-exchange methods tested 4°C storage is preferable to −20°C (stability 14–21 days vs. 4–10 days). For studies where long-term stability is required, samples should be stored at −70°C or colder.

To the Editor: In a recent study by Little et al. (1), the story of C-peptide standardization was left somewhat uncertain with the problem of 2 reference methods providing different C-peptide concentrations. Although very well correlated ( r 2 = 0.986), there was a bias of approximately 20% between the Diabetes Diagnostic Laboratory (DDL)1 method (operated in 2 different laboratories in the US) and the National Metrology Institute of Japan (NMIJ; y = 0.7824x − 0.0202). There were differences in the procedures and in the labeled internal standards (ISs). The NMIJ method was traceable to the NMIJ Certified Reference Material (6901-b) (2), whereas the DDL method was traceable to the IS developed in Dr. Stein's Laboratory in …

An application of ion exchange chromatography for C-peptide analysis is described here. At the stage of C-peptide isolation, a strong cation exchanger (SP HP or MonoS) was used to purify the analyte from ballast proteins and peptides. The conditions of ion-exchange chromatographic separations were optimized using theoretical modeling of the net surface electric charge of the peptide as a function of pH. The purified and concentrated sample was further subjected to LC-MS/MS. In order to improve the reliability of analysis, two fragment ions were monitored simultaneously both for native C-peptide and internal standard, isotopically labeled C-peptides analogues (fragments with m/z of 927.7 and 147.2). Using ion-exchange chromatography, it became possible to process larger sample volumes, important for testing patients with very low C peptide levels, compared to currently used solid phase extraction methods.

BACKGROUND The Diabetes Control and Complications Trial (DCCT) and United Kingdom Prospective Diabetes Study (UKPDS) established the importance of hemoglobin A1c (Hb A1c) as a predictor of outcome in patients with diabetes mellitus. In 1994, the American Diabetes Association began recommending specific Hb A1c targets, but lack of comparability among assays limited the ability of clinicians to use these targets. The National Glycohemoglobin Standardization Program (NGSP) was implemented in 1996 to standardize Hb A1c results to those of the DCCT/UKPDS. CONTENT The NGSP certifies manufacturers of Hb A1c methods as traceable to the DCCT. The certification criteria have been tightened over time and the NGSP has worked with the College of American Pathologists in tightening proficiency-testing requirements. As a result, variability of Hb A1c results among clinical laboratories has been considerably reduced. The IFCC has developed a reference system for Hb A1c that facilitates metrological traceability to a higher order. The NGSP maintains traceability to the IFCC network via ongoing sample comparisons. There has been controversy over whether to report Hb A1c results in IFCC or NGSP units, or as estimated average glucose. Individual countries are making this decision. SUMMARY Variability among Hb A1c results has been greatly reduced. Not all countries will report Hb A1c in the same units, but there are established equations that enable conversion between different units. Hb A1c is now recommended for diagnosing diabetes, further accentuating the need for optimal assay performance. The NGSP will continue efforts to improve Hb A1c testing to ensure that clinical needs are met.

Development of efficient and safe intervention strategies for preserving and/or restoring endogenous insulin production in type 1 diabetes has encountered a wide range of challenges, including lack of standardized trial protocols and of consensus on appropriate efficacy endpoints. For the greatest part, difficulties resided in choosing the most suitable assay(s) and parameter(s) to assess the beta-cell function. It is now an accepted approach to evaluate endogenous insulin secretion by measuring C-peptide levels (with highly sensitive and normalized measurement methods) in response to a physiologic stimulus (liquid mixed-meal) under standardized conditions. Preventive interventions mandate the identification of well-defined, reliable and validated mechanistic or immunological markers of efficacy that would correlate with (and predict) the clinical outcome. This has not been consistently achieved to date. However, it has been generally agreed that for preventive studies performed very early in the disease course (in subjects without signs of autoimmunity against beta-cells) development of two or more islet related autoantibodies could be employed as biomarkers of disease and thereafter, diagnostic criteria of diabetes serve as suitable endpoints.This report summarizes the conclusions of the D-Cure workshop of international experts held in Barcelona in April 2007 and the current recommendations and updates in the field.

Glycated hemoglobin (GHB), reported as HbA 1c , has been used to monitor glycemic control in patients with diabetes for many years. The critical importance of the test was not fully realized until the Diabetes Control and Complications Trial (DCCT) 1 showed a strong relationship between HbA 1c and risk for diabetes complications. After the DCCT was completed, specific diabetes treatment goals were established 2 ; a general goal for most patients with diabetes was an HbA 1c of

Hemoglobin A1c (HbA1c) is used routinely to monitor long-term glycemic control in people with diabetes mellitus, as HbA1c is related directly to risks for diabetic complications. The accuracy of HbA1c methods can be affected adversely by the presence of hemoglobin (Hb) variants or elevated levels of fetal hemoglobin (HbF). The effect of each variant or elevated HbF must be examined with each specific method. The most common Hb variants worldwide are HbS, HbE, HbC, and HbD. All of these Hb variants have single amino acid substitutions in the Hb β chain. HbF is the major hemoglobin during intrauterine life; by the end of the first year, HbF falls to values close to adult levels of approximately 1%. However, elevated HbF levels can occur in certain pathologic conditions or with hereditary persistence of fetal hemoglobin. In a series of publications over the past several years, the effects of these four most common Hb variants and elevated HbF have been described. There are clinically significant interferences with some methods for each of these variants. A summary is given showing which methods are affected by the presence of the heterozygous variants S, E, C, and D and elevated HbF. Methods are divided by type (immunoassay, ion-exchange high-performance liquid chromatography, boronate affinity, other) with an indication of whether the result is artificially increased or decreased by the presence of a Hb variant. Laboratorians should be aware of the limitations of their method with respect to these interferences.

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.

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: Inaccurate blood glucsoe monitoring systems (BGMSs) can lead to adverse health effects. The Diabetes Technology Society (DTS) Surveillance Program for cleared BGMSs is intended to protect people with diabetes from inaccurate, unreliable BGMS products that are currently on the market in the United States. The Surveillance Program will provide an independent assessment of the analytical performance of cleared BGMSs. Methods: The DTS BGMS Surveillance Program Steering Committee included experts in glucose monitoring, surveillance testing, and regulatory science. Over one year, the committee engaged in meetings and teleconferences aiming to describe how to conduct BGMS surveillance studies in a scientifically sound manner that is in compliance with good clinical practice and all relevant regulations. Results: A clinical surveillance protocol was created that contains performance targets and analytical accuracy-testing studies with marketed BGMS products conducted by qualified clinical and laboratory sites. This protocol entitled “Protocol for the Diabetes Technology Society Blood Glucose Monitor System Surveillance Program” is attached as supplementary material. Conclusion: This program is needed because currently once a BGMS product has been cleared for use by the FDA, no systematic postmarket Surveillance Program exists that can monitor analytical performance and detect potential problems. This protocol will allow identification of inaccurate and unreliable BGMSs currently available on the US market. The DTS Surveillance Program will provide BGMS manufacturers a benchmark to understand the postmarket analytical performance of their products. Furthermore, patients, health care professionals, payers, and regulatory agencies will be able to use the results of the study to make informed decisions to, respectively, select, prescribe, finance, and regulate BGMSs on the market.

A liquid chromatography with mass spectrometry on-line platform that includes the orthogonal techniques of ion exchange and reversed phase chromatography is applied for C-peptide analysis. Additional improvement is achieved by the subsequent application of cation- and anion-exchange purification steps that allow for isolating components that have their isoelectric points in a narrow pH range before final reversed-phase mass spectrometry analysis. The utility of this approach for isolating fractions in the desired “pI window” for profiling complex mixtures is discussed.

Background Beta-thalassemia minor (BTM) is a common benign condition that can be present in patients with diabetes mellitus. There are conflicting reports about the effect of BTM on glycated hemoglobin (gHb) measurements. We evaluated 6 gHb methods using samples from non-diabetic subjects with BTM. Methods Samples submitted for hemoglobin phenotype analysis were evaluated. A total of 57 samples (30 controls and 27 with BTM) from non-diabetic subjects were selected. GHb analysis was performed by Tosoh A1c 2.2+, Primus CLC 330, Bayer DCA 2000, Beckman Coulter, Synchron CX7 and LX20, and Roche Tina-quant II assays. Results The A1c 2.2+, CLC 330, DCA 2000 and Tina-quant II assays showed no statistically significant difference between the control and BTM groups. In contrast, BTM results were significantly higher than controls on the Synchron CX7 analyzer and borderline significant on the Synchron LX20 (p=0.051). Further investigation demonstrated an increase in Synchron %HbA1c results with decreasing hemoglobin concentrations. Conclusions In this study using samples from subjects with normal or near-normal gHb, BTM does not affect gHb measurements per se. However, the Synchron methods yielded higher results for samples with lower hemoglobin concentrations, like those that can be seen in BTM. The Synchron method was improved at the end of 2003, which minimized this problem.

Monitoring of glycemic status, as performed by patients and health care providers, is considered a cornerstone of diabetes care. Results of monitoring are used to assess the efficacy of therapy and to make adjustments in diet, exercise, and medications in order to achieve the best possible blood glucose control. The purpose of this review is to summarize current knowledge about the tests used most widely in monitoring the glycemic status of people with diabetes. The review addresses both patient- and physician/laboratory-based testing, and it includes tests of urine glucose and ketones and tests of blood glucose and glycated proteins (hemoglobin and serum proteins). The major emphasis is on the advantages and limitations of each test for routine clinical practice. Use of these tests for diabetes screening and diagnosis will not be addressed in this review. Since this review was first published in 1995, there have been many advances in the field, most notably standardization of glycated hemoglobin testing and new approaches to self-monitoring of blood glucose (SMBG), including minimally invasive continuous glucose monitoring over hours to days at a time. These and other advances are presented in detail in a recent report that was prepared by the National Academy of Clinical Biochemistry (NACB) and published as an American Diabetes Association (ADA) position statement (1). This review will attempt to complement, rather than duplicate, the material in the NACB report. If there was an ideal method of monitoring glycemic status, it might be a small noninvasive device, perhaps similar to a wristwatch that people with diabetes could wear to continuously monitor their blood glucose level. The device would warn of impending hypoglycemia. It also would store blood glucose data and perform a variety of calculations such as hourly, daily, weekly, or monthly blood glucose averages. Unfortunately, such a monitoring device is …

The Centers for Disease Control and Prevention, or CDC, has a long history of providing traceability in clinical laboratory medicine. Early work was to develop reference methods for important clinical analytes. When the National Cholesterol Education Program issued recommendations for physicians and clinical laboratories for measurement of lipids and lipoproteins, CDC formed the Cholesterol Reference Method Laboratory Network (CRMLN) to provide manufacturers with access to the accuracy bases. The CRMLN assists manufacturers with calibration of diagnostic products to ensure traceability to higher-order technology. A certification program for manufacturers assures the clinical laboratory community that these products are accurate and precise. The CRMLN model for traceability has been applied to other networks, notably the National Glycohemoglobin Standardization Program.

Background: Previous studies have shown interference with HbA1c measurement from the 4 most common heterozygous Hb variants (HbAS, HbAE, HbAC, and HbAD) with some assay methods. Here we examine analytical interference from 49 different less common variants with 7 different HbA1c methods using various method principles. Methods: Hb variants were screened using the Bio-Rad Variant or Variant II beta thal short program, confirmed by alkaline and acid electrophoresis, and identified by sequence analysis. The Trinity ultra2 boronate affinity high-performance liquid chromatography (HPLC) method and Roche Tinaquant immunoassay were used as primary and secondary comparative methods, respectively, since these methods are least likely to show interference from Hb variants. Other methods included were the Tosoh G7 and G8, Bio-Rad D-10 and Variant II Turbo, Diazyme Enzymatic, and Sebia Capillarys 2 Flex Piercing. To eliminate any inherent calibration bias, results for each method were adjusted using regression verses the ultra2 with nonvariant samples. Each method’s calibration-adjusted results were compared and judged to be acceptable if within the 99% prediction interval of the regression line for nonvariant samples. Results: Almost all variant samples were recognized as such by the ion-exchange HPLC methods by the presence of abnormal peaks or results outside the reportable range. For most variants, interference was seen with 1 or more of the ion-exchange methods. Following manufacturer instructions for interpretation of chromatograms usually, but not always, prevented reporting of inaccurate results. Results: Laboratories must be cautious about reporting results when the presence of a variant is suspected.

OBJECTIVE— To define the relationship between HbA1c and plasma glucose (PG) levels in patients with type 1 diabetes using data from the Diabetes Control and Complications Trial (DCCT). RESEARCH DESIGN AND METHODS— The DCCT was a multicenter, randomized clinical trial designed to compare intensive and conventional therapies and their relative effects on the development and progression of diabetic complications in patients with type 1 diabetes. Quarterly HbA1c and corresponding seven-point capillary blood glucose profiles (premeal, postmeal, and bedtime) obtained in the DCCT were analyzed to define the relationship between HbA1c and PG. Only data from complete profiles with corresponding HbA1c were used (n = 26,056). Of the 1,441 subjects who participated in the study, 2 were excluded due to missing data. Mean plasma glucose (MPG) was estimated by multiplying capillary blood glucose by 1.11. Linear regression analysis weighted by the number of observations per subject was used to correlate MPG and HbA1c. RESULTS— Linear regression analysis, using MPG and HbA1c summarized by patient (n = 1,439), produced a relationship of MPG (mmol/l) = (1.98 ○1 HbA1c) - 4.29 or MPG (mg/dl) = (35.6 ○1 HbA1c) - 77.3, r = 0.82). Among individual time points, afternoon and evening PG (postlunch, predinner, postdinner, and bedtime) showed higher correlations with HbA1c than the morning time points (prebreakfast, postbreakfast, and prelunch). CONCLUSIONS— We have defined the relationship between HbA1c and PG as assessed in the DCCT. Knowing this relationship can help patients with diabetes and their healthcare providers set day-to-day targets for PG to achieve specific HbA1c goals.

We read with concern the article by Lewis et al. (1) regarding HbA1c analysis in the Vitamin D and Type 2 Diabetes (D2d) Study. Although the article focused on reporting the presence of hemoglobin (Hb) variants after incidental detection of variants by HbA1c high-performance liquid chromatography (HPLC) methods, there was also clear mention of a lack of interference from HbS and HbC with the HbA1c assay used for the study—the Tosoh G8 HPLC. Unfortunately, although the authors claim that there is no interference of these common Hb variants with the Tosoh G8 method, there is clear evidence to the contrary. Our study (2) clearly showed a statistically and clinically significant bias in results from this …

BACKGROUND A major objective of the IFCC Task Force on Implementation of HbA1c Standardization is to develop a model to define quality targets for glycated hemoglobin (Hb A1c). METHODS Two generic models, biological variation and sigma-metrics, are investigated. We selected variables in the models for Hb A1c and used data of external quality assurance/proficiency testing programs to evaluate the suitability of the models to set and evaluate quality targets within and between laboratories. RESULTS In the biological variation model, 48% of individual laboratories and none of the 26 instrument groups met the minimum performance criterion. In the sigma-metrics model, with a total allowable error (TAE) set at 5 mmol/mol (0.46% NGSP), 77% of the individual laboratories and 12 of 26 instrument groups met the 2σ criterion. CONCLUSIONS The biological variation and sigma-metrics models were demonstrated to be suitable for setting and evaluating quality targets within and between laboratories. The sigma-metrics model is more flexible, as both the TAE and the risk of failure can be adjusted to the situation—for example, requirements related to diagnosis/monitoring or international authorities. With the aim of reaching (inter)national consensus on advice regarding quality targets for Hb A1c, the Task Force suggests the sigma-metrics model as the model of choice, with default values of 5 mmol/mol (0.46%) for TAE and risk levels of 2σ and 4σ for routine laboratories and laboratories performing clinical trials, respectively. These goals should serve as a starting point for discussion with international stakeholders in the field of diabetes.

Two very interesting articles on hemoglobin A1c (Hb A1c)2 method performance appear in this issue of Clinical Chemistry . Woodworth et al. (1) use Hb A1c as an example of how the risk of reporting inaccurate results can be estimated to guide individualized QC strategies. They assess the risk of reporting unreliable Hb A1c results with 6 different methods in 4 academic medical centers; 5 are laboratory instruments and 1 is a point-of-care (POC) method. Patient-weighted σ metrics were calculated on the basis of 1–2s QC rules with an average of 1 QC for every 100 samples. The authors found considerable differences in the risk of reporting unreliable results among the methods used at these sites, and that only 1 method, the Capillarys2 Flex Piercing, achieved a patient-weighted σ metric >3 at a total error allowable (TEa) of 6%. This total error limit is also used for College of American Pathologists (CAP) proficiency testing and National Glycohemoglobin Standardization Program (NGSP) certification and is considered optimal for clinical care at this time. This means that for all but the aforementioned method, “maximum QC (three levels, three times per day) should be performed to achieve the necessary error detection.” Of note was that for some methods there was a substantial amount of bias (up to 5.8% relative for values within the reference interval), and CV values were higher than the recommended 2% for either the high or low QC for 3 of the methods studied (2). The maximum number of Hb A1c results out of 100 expected to be unreliable from an out-of-control condition at TEa of 6% ranged from 0.60 to 71.48 (!), and for 2 methods the number of results expected to be unreliable was >19 of 100 even when …