Calibration by commutable control materials is able to reduce inter-method differences of current high-performance methods for HbA₂

Background: Most of the current methods used for the determination of HbA₂ seem not well aligned. A comparison among the best performing techniques and the commutability of some control materials currently available and under development has been evaluated.

Methods: Forty blood samples were analyzed in duplicate over two separate days by different HPLC and capillary electrophoresis systems. The commutabilities of different control materials (NIBSC WHO reagent, Bio-Rad Lyphochek, and home prepared lyophilized controls RP1-3) have been assessed by analyzing the controls in quadruplicate over two consecutive days together with the blood samples.

Results: The mean within-run imprecision of HbA₂ measurement on blood samples (CV, %) was between 0.6% and 10.1% for HbA₂ values <3.5%, and between 1.1 and 3.1 for HbA₂≥3.5%. The different methods were highly correlated (r between 0.9941 and 0.9995) although biased each other. The NIBSC WHO reagent was found not commutable in 15 over 28 comparisons, the Lyphochek 2 in 18/28, and RP3 in 4/28. Recalibration of all methods by RP1 and RP2 materials was able to reduce the overall variability from 6.8% to 3.4% at HbA₂≤3.0% and from 6.7% to 3.0% at HbA₂≥4.6%.

Conclusion: The use of adequate commutable control materials as calibrators may reduce the inter-method variability of routine methods to an extent closer to the current analytical goals of bias based on biological variability.