The relationship between glycosylated haemoglobin levels and various degrees of glucose intolerance

To assess the use of glycosylated haemoglobin to discriminate between various degrees of glucose intolerance, glycosylated haemoglobin levels were determined in 107 subjects (48 males and 59 females, age range 18-80 years). Following a 75 g oral glucose tolerance test and according to World Health Organization criteria, subjects were classified as normal (n = 32), diabetic (n = 46) or as having impaired glucose tolerance (n = 29). Mean glycosylated haemoglobin levels were 5.8 +/- 1.3% (range 4%-9%) in normal subjects, 7.1 +/- 1.7% in subjects with impaired glucose tolerance (range 4.1%-10.1%) and 10.1 +/- 2.6% (range 4.7%-18.8%) in diabetic patients. The difference between the groups was highly significant (p less than 0.01). Twelve per cent of normal subjects exceeded and 52% of subjects with impaired glucose tolerance fell below 7.4% (mean +/- 2SD, considered as the upper limit of normal values). A significant correlation was observed between glycosylated haemoglobin values and fasting blood glucose (r = 0.68, p less than 0.01). These results provide evidence that glycosylated haemoglobin levels are influenced by slightly reduced carbohydrate tolerance. Glycosylated haemoglobin may be a useful test to improve the specificity of the oral glucose load to select and to follow-up subjects with impaired glucose tolerance.