A1C Cut Points to Define Various Glucose Intolerance Groups in Asian Indians

Abstract

OBJECTIVE— To determine A1C cut points for glucose intolerance in Asian Indians. RESEARCH DESIGN AND METHODS— A total of 2,188 participants without known diabetes were randomly selected from the Chennai Urban Rural Epidemiology Study. All had fasting plasma glucose (FPG) and 2-h postload plasma glucose measurements after a 75-g load and were classified as having impaired fasting glucose (IFG) (American Diabetes Association [ADA] criteria, FPG5.5 and7 mmol/l, and World Health Organization [WHO] criteria, FPG 6.1 and7 mmol/l), impaired glucose tolerance (IGT) (2-h postload plasma glucose7.8 and 11.1 mmol/l), or diabetes (FPG 7 mmol/l and/or 2-h postload plasma glucose 11.1 mmol/ l). A1C was measured using the Bio-Rad Variant machine. Based on receiver operating characteristic curves, optimum sensitivity and specificity were derived for defining A1C cut points for diabetes, IGT, and IFG. RESULTS— Mean SD values of A1C among subjects with normal glucose tolerance, IGT, and diabetes were 5.5 0.4, 5.9 0.6, and 8.3 2.0%, respectively (Ptrend 0.001) with considerable overlap. To identify diabetes based on 2-h postload plasma glucose, the A1C cut point of 6.1% had an area under the curve (AUC) of 0.941 with 88.0% sensitivity and 87.9% specificity. When diabetes was defined as FPG 7.0 mmol/l, the A1C cut point was 6.4% (AUC 0.966, sensitivity 93.3%, and specificity 92.3%). For IGT, AUC 0.708; for IFG, AUC 0.632 (WHO criteria) and 0.708 (ADA criteria), and the A1C cut point was 5.6%. CONCLUSIONS— In Asian Indians, A1C cut points of 6.1 and 6.4% defined diabetes by 2-h postload plasma glucose or FPG criteria, respectively. A value of 5.6% optimally identified IGT or IFG but was 70% accurate.