Glycosylated haemoglobin as an alternative to the glucose tolerance test for the diagnosis of diabetes mellitus.

A comparison was made between the results of a standard 75 g oral glucose tolerance test and total haemoglobin A1 in 168 subjects referred by their general practitioners for the diagnosis of diabetes mellitus. The subjects were classified as having normal, impaired or diabetic glucose tolerance using WHO criteria. Of 108 subjects with normal glucose tolerance only three had haemoglobin A1 concentrations over 8%. Of 10 with impaired glucose tolerance two had haemoglobin A1 concentrations over 8%. Of 47 with diabetic responses, eight had haemoglobin A1 concentrations below 9%. There was a significant difference between the haemoglobin A1 concentration when fasting and that 2 hours after the glucose load in the subjects with a diabetic glucose tolerance response, but no significant difference between the two values in the other subjects.