Glucose tolerance test and glycosylated haemoglobin measurement for diagnosis of diabetes mellitus--an assessment of the criteria of the WHO Expert Committee on Diabetes Mellitus 1980.

Fasting glycosylated haemoglobin was analysed in 535 consecutive patients having an oral 75 g glucose tolerance test for diagnostic purposes. A reference range for fasting glycosylated haemoglobin was established from patients with a non-diabetic glucose tolerance test as defined by the World Health Organisation Expert Committee on Diabetes Mellitus. The predictive value of a glycosylated haemoglobin of over 10.0% (mean normal +/- 3 SD) for detecting a diabetic glucose tolerance test was 89% but sensitivity was only 43%. A raised glycosylated haemoglobin is useful for confirming the diagnosis of diabetes mellitus in patients with long-standing hyperglycaemia but glycosylated haemoglobin is within the reference range in many patients with newly developed diabetes or other minor abnormalities of glucose tolerance. The glucose tolerance test must remain the test of choice in these patients.