Measurement of hemoglobin A1c from filter papers for population-based studies.

BACKGROUND Stability and transport challenges make hemoglobin (Hb) A(1c) measurement from EDTA whole blood (WB) inconvenient and costly for large-scale population studies. This study investigated Hb A(1c) measurement from WB blotted on filter paper (FP) in a Level I National Glycohemoglobin Standardization Program (NGSP)-accredited laboratory. METHODS Three Bio-Rad Variant™ II HPLC instruments and WB and FP specimens were used. Precision, accuracy, linearity, and readable total area of the 6.5-min (β-thalassemia method) Variant II HbA(2)/HbA(1c) Dual Program were assessed. Hb A(1c) stability was measured using in-house FP QC samples. The INTERHEART (a study of the effect of potentially modifiable risk factors associated with myocardial infarction in 52 countries) and CURE (Clopidogrel in Unstable Angina to Prevent Recurrent Events) studies provided chromatographs for morphometric analyses and interoperator variability experiments. Statistical analyses were performed to assess long-term sample stability, WB vs FP agreement, and significance of Hb A(1c) peak integration. RESULTS Intra- and interassay CVs were ≤2.00%. Total area counts between 0.8 and 5.5 × 10(6) μV/s produced accurate Hb A(1c) results. The regression equation for agreement between WB(x) and FP(y) was as follows: y = 0.933x + 0.4 (n = 85). FP QC samples stored at -70 °C and tested over approximately 3 years yielded CVs of 1.72%-2.73% and regression equations with slopes of -1.08 × 10(-4) to 7.81 × 10(-4). The CURE study, with better preanalytical preparation, achieved a 97% reportable rate, and the reportable rate of the INTERHEART study was 85%. CONCLUSIONS The FP collection method described provided accurate, robust, and reproducible measurement of Hb A(1c) using the Bio-Rad Variant II HPLC autoanalyzer when FP specimens were prepared according to standardized protocols, and analyses were performed in an NGSP-certified laboratory, supporting the use of FP collection cards in large multinational studies.