Comparison between a rapid glycohaemoglobin (HbA1c) immunoassay and other indices of glycaemic control

The aims of the study were to compare glycohaemoglobin (HbA1c) values measured by DCA (a benchtop analyzer primarily designed for within-clinic rapid HbA1c determination) to a reference HbA1c method and home blood glucose monitoring, and to explore the possibility of an uniform expression of data. A total of 103 blood samples and the corresponding mean capillary glucose values (4.4±1.2 tests/day) of the preceding 2 months were collected from 34 insulin-dependent diabetic adults. We measured the correlations and agreements using the residual plots method and regression equations between HbA1c measured by DCA and high-pressure liquid chromatography (HPLC), and between DCA and capillary glucose values. A highly significant correlation (r2=0.85,P<0.001) and an acceptable agreement (97% of values within 2 SD of the mean difference of 0.9%±0.4%) was found between DCA and HPLC values. The regression equation calculated on the first half of the cases was: DCA (%)=0.72 HPLC (%)+1.38. Of DCA values expressed in HPLC terms using this equation 87% fell within a clinically acceptable confidence interval when compared with measured HPLC data. A significant correlation (r2=0.40,P<0.01) was found between DCA and capillary glucose values, and the regression equation was: DCA (%)=0.34 capillary glucose (mM)+4.44. Of glycaemic levels calculated from DCA values using this formula 82% fell within a clinically acceptable error range when compared with measured glycaemic values. We conclude that the three methods of assessment of diabetes control are well correlated and that it is possible, with a degree of precision acceptable for the clinical setting, to express all data in uniform units, e.g. mM of capillary glucose or percentage of HPLC-HbA1c, though a simple correspondence table based on our transfer equations may be clinically sufficient and more handy.