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 °C. Affinity chromatography, HPLC, electrophoresis and immunoassay detected no changes following 18 months storage at -84 and -20 °C. Samples for HPLC are stable at 4 °C for one year, and 5 years at -20 °C. For the other three methods, samples are stable for 5 years at 4 °C. At 4 °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 lc value by HPLC, may contribute, in the interim, to the standardized interpretation of long term diabetic control.

SUMMARY. Stable lyophilized ethylenediaminetetra-acetic acid (EDTA)-blood haemolysates were applied in an external quality assurance programme (SKZL, The Netherlands) for glycohaemoglobin assays in 101 laboratories using 12 methods. The mean intralaboratory day-to-day coefficient of variation (CY), calculated from the assay of 12 unidentified pairs over a period of 1 year, was 5·2010 (range: 0.2-28 0 7 ) .Forty-seven per cent of laboratories did not meet the criterion of CY < 5010, whereas 68% did not meet the clinically more desirable 3.3-3 0 6 % . Linearity, as derived from the analysis of five combinations of two haemolysates with low and high glycohaemoglobin percentages over 6 months, was excellent (mean correlation coefficient 0·9953; range: 0.9188-0 0 9 9 9 9 ) . Analysis of two samples with high and low glycohaemoglobin percentages gave mean interlaboratory coefficients of variation of 10% for one method performed by several laboratories and 22% for all methods performed by all laboratories. It is concluded that the majority of laboratories do not meet the clinically desirable intralaboratory precision and that an unacceptably high interlaboratory precision exists.

No abstract

No abstract

One hundred eleven laboratories, using 21 different methods based on five different principles, determined glycohemoglobin (GHb) percentages in two identical series of six lyophilized hemolysates and three similarly processed calibrators, distributed 3 months apart. To assign GHb percentages to calibrators, we used HbA1c results from nine participants who used the Bio-Rad Diamat high-performance liquid chromatographic method. Three-point calibration with assigned values improved mean intralaboratory variation (CV) from 6.6% to 3.5%. For samples with low (5.5%) and high (14.1%) GHb percentages, respectively, calibration decreased interlaboratory variation per method (from 10% to 4% and from 6% to 3%), inter-method variation (from 18% to 4% and from 16% to 3%), and overall interlaboratory variation (from 25% to 7% and from 15% to 4%). Without calibration, 71% of the laboratories did not meet the clinically desirable intralaboratory CV of 3.5%; calibration reduced this proportion to 39%. We conclude that, irrespective of the analytical method used, calibration greatly reduces all sources of GHb variation.