Characteristics of labile HbA1 in erythrocytes from normals and diabetics.

Incubation of erythrocytes from diabetic patients and non-diabetic persons in 0.15 mol/l saline at 37 degrees C was followed by a decrease in ion-exchange microcolumn determined HbA1 only during the first 4 h. The fraction removed was denoted as labile HbA1 and the remaining fraction as stable HbA1. Incubation in saline overnight at 20 degrees C did not completely remove the labile fraction. Incubation in saline overnight at 4 degrees C yielded only a slight decrease in labile HbA1. Incubation in saline containing various glucose concentrations (up to 100 mmol/l) produced increasing amounts of HbA1 during the first 3-4 h after which an equilibrium was reached. In both normal and diabetic erythrocytes incubated for 3-4 h we found a linear relationship between changes in labile HbA1 and glucose concentration. The degree of increase in labile HbA1 was the same in normals and diabetics and not dependent on pre-existing normal or moderately increased stable HbA1. In the blood from non-diabetics (n = 30) labile HbA1 was 0.5 +/- 0.3% (mean +/- SD) and in diabetics (n = 80) 1.6 +/- 0.8%. The correlation between labile HbA1 and simultaneously determined blood glucose was r = 0.72.