Revaluation of biological variation of glycated haemoglobin (HbA1c) using an accurately designed protocol and an assay traceable to the IFCC reference system

Background: Glycated hemoglobin (HbA1c) has a key role for diagnosing diabetes and monitoring glycemic state. As recently reviewed, available data on HbA1c biological variation show marked heterogeneity. Here we experimentally revaluated these data using a well designed protocol. Methods: We took five EDTA whole blood specimens from 18 apparently healthy subjects on the same day, every two weeks for two months. Samples were stored at 1280 \ub0C until analysis and assayed in duplicate in a single run by Roche Tina-quant\uae Gen.2 immunoassay. Data were analyzed by the ANOVA. To assess the assay traceability to the IFCC reference method, we preliminarily carried out a correlation experiment. Results: The bias (mean\ub1SD) of the Roche immunoassay was 0.3%\ub10.7%, confirming the traceability of the employed assay. No difference was found in HbA1c values between men and women. Within- and betweensubject CV were 2.5% and 7.1%, respectively. Derived desirable analytical goals for imprecision, bias, and total error resulted 1.3%, 1.9%, and 3.9%, respectively. HbA1c hadmarked individuality, limiting the use of populationbased reference limits for test interpretation. The estimated critical difference was ~10%. Conclusions: For the first time we defined biological variation and derived indices for the clinical application of HbA1c measurements using an accurately designed protocol and an assay standardized according to the IFCC