Hemoglobin A_Ic as an indicator of the degree of glucose intolerance in diabetes

Hemoglobin A_Ic concentration, fasting blood sugar, response to an oral glucose tolerance test, and skeletal muscle capillary basement membrane thickness were measured in diabetic patients. Hemoglobin A_Ic concentration correlates with both response to a glucose tolerance test (r = 0.82, p < 0.001) and fasting blood sugar (r = 0.62, p < 0.001). The correlation of hemoglobin A_Ic concentration with glucose tolerance is independent of fasting blood sugar concentration (partial r = 0.61, p < 0.005), whereas that of hemoglobin A_Ic with fasting blood sugar probably reflects the relationship between fasting blood sugar levels and glucose tolerance (partial r = 0.22, p < 0.05). Hemoglobin A_Ic levels do not correlate with basement membrane thickness (r = 0.15, p < 0.05).