Identifying Dysglycemic States in Older Adults: Implications of the Emerging Use of Hemoglobin A1c

Context: Hemoglobin A1c (A1c) was recently added to the diagnostic criteria for diabetes and prediabetes. Objective: Our objective was to examine performance of A1c in comparison with fasting plasma glucose (FPG) in diagnosing dysglycemia in older adults. Design and Setting: We conducted a cross-sectional analysis of data from the Health, Aging, and Body Composition study at yr 4 (2000-2001) when FPG and standardized A1c measurements were available. Participants: Of 3075 persons (aged 70-79 yr, 48% men, 42% Black) at study entry, 1865 participants without known diabetes who had appropriate measures were included. Main outcome measures: Sensitivity and specificity of A1c-based diagnoses were compared with those based on FPG and the proportion of participants identified with dysglycemia by each measure. Results: Of all participants, 2.7 and 3.1% had undiagnosed diabetes by FPG >= 126 mg/dl and A1c >= 6.5%, respectively. Among the remaining participants, 21.1% had prediabetes by impaired fasting glucose (>= 100 mg/dl) and 22.2% by A1c >= 5.7%. Roughly one third of individuals with diabetes and prediabetes were identified by either FPG or A1c alone and by both tests simultaneously. Sensitivities and specificities of A1c compared with FPG were 56.9 and 98.4% for diabetes and 47.0 and 84.5% for prediabetes, respectively. Blacks and women were more likely to be identified with dysglycemia by A1c than FPG. Conclusions: In this older population, we found considerable discordance between FPG- and A1c-based diagnosis of diabetes and prediabetes, with differences accentuated by race and gender. Broad implementation of A1c to diagnose dysglycemic states may substantially alter the epidemiology of these conditions in older Americans. (J Clin Endocrinol Metab 95: 5289-5295, 2010)