The Importance of Determining Irreversibly Glycosylated Hemoglobin in Diabetics

The concentration of glycohemoglobins (HbA_1(a+b+c), HbA₁,) was measured before and after incubation of normal and diabetic erythrocytes for 6 h at 37°C in saline. This procedure removes as much as 80-90% of the labile glucose-HbA₀ adduct (labile HbA₁,), thus allowing accurate estimation of irreversibly glycosylated hemoglobin (stable HbA₁,). The concentration of HbA₁ measured before such an incubation is total HbA₁, (stable + labile). We determined the concentration of total, stable, and labile HbA₁, in the same blood samples used to measure fasting plasma glucose (FPG) every day, for 4 consecutive days, in two groups of hospitalized insulin-treated diabetics. Group A subjects (N = 7) were type I, C-peptide negative, unstable diabetics, while group B subjects (N = 15) were type II, C-peptide positive, stable diabetics. Individual day-to-day variations of total HbA₁, were wide in group A (Δ = 1.58 ± 0.14%), and slight in group B (Δ = 0.12 ± 0.01%; P < 0.001), paralleling similar plasma glucose fluctuations. Day-to-day variations of stable HbA₁, were virtually absent not only in group B subjects with stable glycemic values (Δ = 0.08 ± 0.01%), but also in those of group A with marked glycemic instability (Δ = 0.07 ± 0.01%; P = NS). Day-to-day variations of labile HbA₁, were marked in group A (Δ = 1.31 ± 0.14%), but negligible in group B (Δ = 0.15 ± 0.03%; P < 0.001). On admission, FPG correlated with labile HbA₁, in group A (r = 0.89) and B (r = 0.71). FPG correlated with stable HbA₁, in group B (r = 0.73) but not in group A subjects and with total HbA₁, more closely in group B (r = 0.73) than in A (r = 0.61). A very close correlation was found between the concentration of total and labile HbA₁ in subjects of group B (r = 0.82). In group B, fasting, post-breakfast, and mean daily plasma glucose values, determined every 3-6 days during the 2 mo before admission, significantly correlated both with total and stable HbA₁ determined on admission, while in group A they did not. In group A, the correlation was significant when stable instead of total HbA₁ was considered. We conclude that the significant fluctuations of total HbA₁ reduce its value as an index of long-term control in unstable diabetics. On the other hand, a single determination of stable HbA₁, totally independent of simultaneous blood glucose values, closely reflects blood glucose control over the previous 2 mo. We propose routine estimation of stable HbA₁, which is simple and straightforward, to carry out follow-up studies of unstable diabetics.