Elevated HbA1c and Fasting Plasma Glucose in Predicting Diabetes Incidence Among Older Adults

OBJECTIVE To determine which measures-impaired fasting glucose (IFG), elevated HbA1c, or both-best predict incident diabetes in older adults. RESEARCH DESIGN AND METHODS From the Health, Aging, and Body Composition study, we selected individuals without diabetes, and we defined IFG (100-125 mg/dL) and elevated HbA1c (5.7-6.4%) per American Diabetes Association guidelines. Incident diabetes was based on self-report, use of antihyperglycemic medicines, or HbA1c ≥6.5% during 7 years of follow-up. Logistic regression analyses were adjusted for age, sex, race, site, BMI, smoking, blood pressure, and physical activity. Discrimination and calibration were assessed for models with IFG and with both IFG and elevated HbA1c. RESULTS Among 1,690 adults (mean age 76.5, 46% men, 32% black), 183 (10.8%) developed diabetes over 7 years. Adjusted odds ratios of diabetes were 6.2 (95% CI 4.4-8.8) in those with IFG (versus those with fasting plasma glucose [FPG] <100 mg/dL) and 11.3 (7.8-16.4) in those with elevated HbA1c (versus those with HbA1c <5.7%). When FPG and HbA1c were considered together, odds ratios were 3.5 (1.9-6.3) in those with IFG only, 8.0 (4.8-13.2) in those with elevated HbA1c only, and 26.2 (16.3-42.1) in those with both IFG and elevated HbA1c (versus those with normal FPG and HbA1c). Addition of elevated HbA1c to the model with IFG resulted in improved discrimination and calibration. CONCLUSIONS Older adults with both IFG and elevated HbA1c have a substantially increased odds of developing diabetes over 7 years. Combined screening with FPG and HbA1c may identify older adults at very high risk for diabetes.