Bimodality of Glycosylated Hemoglobin Distribution in Pima Indians: Relationship to Fasting Hyperglycemia

Glycosylated hemoglobin (HbA₁) concentrations were determined in 300 Pima Indians aged 15 yr and older. Frequency distributions of HbA, were unimodal in the 15-24-yr-old age group, but were bimodal in those aged 25 yr and over. The bimodality indicated that the subpopulation with diabetes could be identified by the presence of elevated HbA₁ levels. This group was comprised primarily of subjects who also had fasting plasma glucose levels of < 140 mg/dl, but subjects with impaired glucose tolerance without fasting hyperglycemia had HbA₁ levels that were not significantly higher than those with normal glucose tolerance. The prevalence of diabetic retinopathy was much higher in the subgroup with elevated HbA₁ levels and increased with increasing HbA₁ level. HbA₁ levels and triglyceride concentrations showed only a modest association. HbA₁ determinations provided no advantage over fasting or post challenge glucose levels in the diagnosis Of diabetes.