EVALUATION OF A REFERENCE MATERIAL FOR GLYCATED HEMOGLOBIN

The use of lyophilized blood as a reference material for glycated haem oglobin was investigated with respect to IFCC criteria for calibrators and control materials. Ninety-two laboratories, using 11 methods, det ected 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 mon ths 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 t hree methods, samples are stable for 5 years at 4 degrees C. At 4 degr ees C, reconstituted samples are stable for 2 days (HPLC) and 7 days ( other three). Lyophilization does not cause matrix effects and inhomog eneity, since mean glycated haemoglobin and reproducibility for lyophi lized samples and whole blood were similar. The coefficient of variati on 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.