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The high request for vitamin D testing in the last decades has led manufacturers to develop assays on automated immunoassay platforms. The objective of this study was to evaluate the performance of the new Elecsys Vitamin D total III assay for the measurement of total 25(OH)D. A total of 844 serum samples collected in two clinical laboratories were used to evaluate the new Roche Elecsys Vitamin D total III assay. Comparisons with Roche Elecsys Vitamin D total II and liquid chromatography tandem mass spectrometry (LC-MS/MS) were carried out. Additionally, assay imprecision, linearity, matrix effects, biotin interference, cross-reactivity with 24,25(OH)2D3 and 3-epi-25(OH)D3, and outlier rate were evaluated for the Elecsys Vitamin D total III assay. Only the comparison between LC-MS/MS and Roche Elecsys Vitamin D total III achieved the optimal specification for bias (i.e., <3.4%). Imprecision, linearity and matrix effects showed acceptable results. The biotin interference threshold was increased up to 1,200 ng/mL and the outlier rate was low (0.26%). The cross-reactivity with 24,25(OH)2D3 and 3-epi-25(OH)D3 was weak or modest in available patient samples. However, using SRM972a with a high level of 3-epi-25(OH)D3 (enriched) revealed an important cross-reactivity with both Roche Elecsys Vitamin D total II and III assays (+74.7% and +73.7%). In conclusion, the Roche Elecsys Vitamin D total III assay presents several advantages compared to the previous assay generation: higher biotin interference threshold, broader measuring range, and better comparability with LC-MS/MS. However, the cross-reactivity toward 3-epi-25(OH)D3 is still problematic in high titer samples. [ABSTRACT FROM AUTHOR]

Keywords: biotin; ECLIA; immunoassay; method evaluation; thyroglobulin EN biotin ECLIA immunoassay method evaluation thyroglobulin e46 e49 4 01/07/22 20220115 NES 220115 To the Editor, Biotin interference in immunoassays is well-known and researched [[1]]. Exogenous biotin disturbs this interaction, potentially causing falsely decreased results for sandwich immunoassays, such as the Elecsys SP ® sp thyroglobulin (Tg) assay (Roche Diagnostics, Switzerland) [[4]]. Plasma peak concentrations induced by OTC supplements (53-141 ng/mL) or by treatment with high biotin doses (up to 1,160 ng/mL plasma levels) do not exceed the biotin threshold of the Tg2New assay insert or our experimentally confirmed threshold [[1]]. [Extracted from the article]

Background: Long-term stability of analytical performance is required for adequate patient management. We investigated the use of patient data to document test stability, and the relevance of observed instabilities on a surrogate medical outcome. We used multiyear patient and internal quality control (IQC) data from two laboratories for tests to monitor chronic kidney and thyroid disease. Methods: We plotted moving means of the 50th percentiles of stratified patient data and of the daily IQC means. We evaluated observed instabilities based on goals inferred from the analytes' biological variation and investigated their effect on classification of results against reference intervals. Results: Patient and IQC data generally matched well, except for analytes, for which other than analytical variation sources prevailed. Analytical instabilities were predominantly due to reagent/calibrator lot changes, however, for immunoassays also to within-lot instabilities, urging frequent recalibrations. The relevance of biased results on medical decisions ranged from negligible to very pronounced, indicating the need for assessment of analytical performance in relation to quality goals inferred from biological variation. Conclusions: Patient percentiles offer great potential to assess/monitor the medium- to long-term analytical stability of a test within certain constraints. Differences in analytical quality between assays can significantly affect medical outcome. [ABSTRACT FROM AUTHOR]

Serum sex hormone-binding globulin (SHBG) regulates the cellular bioavailability of SHBG-bound steroid hormones. Since variations in SHBG levels may affect the concentration of free, i.e., biologically active testosterone in serum, SHBG levels are commonly measured as a supplement to total testosterone determination. The recently developed electrochemiluminescence Elecsys ® SHBG immunoassay was evaluated analytically on a Modular E170 (Roche Diagnostics, Mannheim, Germany) immunoanalyzer. Major differences in SHBG concentrations have been described among the commercially available methods; we therefore compared the new method with an established SHBG immunoradiometric assay (IRMA) in 99 routine serum samples. To provide reference values to clinicians, SHBG concentration was measured by Elecsys ® in 304 serum samples from healthy volunteers and several relevant clinical subgroups. The within-run and total imprecision coefficients of variation were =2.9% and =3.3%, respectively. Functional sensitivity was at least 0.74 nmol/L. Recoveries after dilution of high-concentration samples in low-titer human serum or in assay diluent were within the range of 85-110%. The Elecsys ® SHBG assay correlated well (r=0.98) with the SHBG immunoradiometric assay, but values were higher for the Elecsys ® assay (Passing Bablok regression analysis: slope 1.14, intercept +2.5). In healthy subjects and clinical subgroups, we confirmed the differences in SHBG values reported in the literature. The Elecsys ® SHBG immunoassay provides precision and reliability in combination with reduced turnaround time. [ABSTRACT FROM AUTHOR]

Background: Investigation of a 61-year-old Caucasian male suffering from fatigue and weight loss led to the finding of a carbohydrate antigen 19-9 (CA 19-9) concentration of 80 kU/L using an ADVIA Centaur analyser. Determination of CA 19-9 on Vidas, AxSYM and Architect i2000 systems gave normal results. His rheumatoid factor concentration was very high (900 kIU/L) and assay interference was suspected. Methods: Besides using several laboratory procedures to show the cause of the interference, we tried to estimate the frequency of the suspected interference. Therefore, two studies were performed. The first was carried out in a multicentre setting using four different CA 19-9 methods on 51 randomly selected samples with high rheumatoid factor concentrations and ten samples containing no or very low rheumatoid factor. In the second study we used heterophilic blocking tubes for 68 routinely analysed samples with CA 19-9 concentrations ranging between 37 and 250 kU/L using an ADVIA Centaur analyser. Results: In the multicentre study we found eight discrepant CA 19-9 results, but only one was clearly due to interference. We showed that the interference detected, just as in the index case, was caused by rheumatoid factor. The other discrepancies could not be explained, but are probably related to method-dependent differences. In the 68 routinely analysed samples, no interference could be shown using the heterophilic blocking tubes. Conclusions: Although interferences in the CA 19-9 assay are not frequent, the ADVIA Centaur system appears to be more sensitive to rheumatoid factor interference. The lack of standardisation remains an important issue for this assay. The determination of CA 19-9 during the follow-up of patients should be performed using a single method. If, however, there is any clinical doubt about a result, CA 19-9 should be determined using another method to exclude possible interferences. Clin Chem Lab Med 2006;44:1137–9. [ABSTRACT FROM AUTHOR]