Evaluation of a reference material for glycated haemoglobin

The use of lyophilized blood as a reference material for glycated haemoglobin was investigated with respect to IFCC criteria for calibrators and control materials. Ninety-two laboratories, using 11 methods, detected no changes in glycated haemoglobin content when the lyophilizate was stored for one year at 4 degrees C. Affinity chromatography, HPLC, electrophoresis and immunoassay detected no changes following 18 months storage at -84 and -20 degrees C. Samples for HPLC are stable at 4 degrees C for one year, and 5 years at -20 degrees C. For the other three methods, samples are stable for 5 years at 4 degrees C. At 4 degrees C, reconstituted samples are stable for 2 days (HPLC) and 7 days (other three). Lyophilization does not cause matrix effects and inhomogeneity, since mean glycated haemoglobin and reproducibility for lyophilized samples and whole blood were similar. The coefficient of variation for vial filling precision was 0.59%. We conclude that lyophilized blood samples can be used as calibrators and control materials. Their use as calibrators, following assignment of the HbA(1c) value by HPLC, may contribute, in the interim, to the standardized interpretation of long term diabetic control.