Glycosylated haemoglobin in the diagnosis of diabetes mellitus in elderly people.

An oral glucose tolerance test (OGTT, 75 g WHO criteria) was applied to healthy elderly subjects (mean age 76 years) within a week of measurement of random blood glucose and glycosylated haemoglobin (HbA1). The 'Corning' method was used to assay HbA1 (established normal range for our laboratory 5-8%). Sixty-five subjects (38 women) of whom 54 were not diabetic on WHO criteria for OGTT participated in the study. Five of the 54 patients with non-diabetic OGTT results had abnormal HbA1 (greater than 8%). These five subjects had no evidence of impaired glucose tolerance. Eleven subjects had diabetic OGTT results of whom only four had raised HbA1 assay results. Seven subjects had normal HbA1 in spite of diabetic OGTT. The mean HbA1 in the group of subjects with normal OGTT (n = 52) was 6.7% (SD 1.05, range 4.6-8.7%). It appears from our study that the normal range of HbA1 in elderly subjects is not markedly different from established normal values. The poor sensitivity (36%) and predictive value (44%) of abnormal HbA1 in detecting diabetes, as shown in our study, would not permit its use for screening purposes nor as a confirmatory test for diabetes in elderly subjects.