Comparison of hemoglobin A1c and hemoglobin A1 in diabetic patients.

Hemoglobin A1 (HbA1) and hemoglobin A1c (HbA1c) values were compared in 934 samples from 686 subjects with diabetes mellitus. Linear regression analysis revealed the two parameters to be highly related with HbA1 = 1.18 HbA1c + 1.67, and a correlation coefficient of 0.97. Samples with HbA1 greater than predicted from the measured HbA1c had been stored significantly longer (approximately 1 day) than other samples, suggesting that sample storage may slightly alter the relationship between these parameters. Serial HbA1 and HbA1c values in all 9 patients for whom data was available from at least 5 time points changed in parallel regardless of the time interval between sampling or the magnitude of the interval change of HbA1c and HbA1. These data indicate that the potentially simpler measurement of HbA1 gives results equivalent to HbA1c for clinical applications.