A1C for Screening and Diagnosis of Type 2 Diabetes in Routine Clinical Practice

OBJECTIVE — To evaluate A1C for screening and diagnosis of undiagnosed type 2 diabetes defined by oral glucose tolerance testing in clinical and general populations. RESEARCH DESIGN AND METHODS — A1C cut offs (5.5 % to rule out diabetes; 7.0 % to rule in diabetes) were derived from a clinical group (Melbourne Pathology [MP] group: n 2,494; undiagnosed diabetes 34.6%) and then evaluated in a population-based sample (AusDiab group: n 6,015; undiagnosed diabetes 4.6%). RESULTS — For diabetes in the MP and AusDiab groups, A1C at 5.5 % gave sensitivities of 98.7 and 83.5%, while A1C at 7.0 % gave specificities of 98.2 and 100%, respectively. Many (61.9–69.3%) with impaired A1C (5.6–6.9%) in both populations had abnormal glucose status. CONCLUSIONS — A1C5.5 % and7.0 % predicts absence or presence of type 2 diabetes, respectively, while at A1C 6.5–6.9 % diabetes is highly probable in clinical and population settings. A high proportion of people with impaired A1C have abnormal glucose status requiring follow-up. Diabetes Care 33:817–819, 2010 W ith current screening tools (fast-ing plasma glucose [FPG] withor without oral glucose tolerance test [OGTT]), the prevalence of undiag-nosed diabetes in Australia remains high (1). A1C provides a practical alternative for screening (2,3). It is more convenient and reproducible than is blood glucose (3,4). As optimal cut offs are still in de-bate, we explore here A1C levels that con-fidently rule out and rule in diabetes in two different Australian populations. RESEARCH DESIGN AND METHODS — We studied two popula-tions. The clinical population, Melbourne Pathology (MP) group, included all patients referred by medical practitioners for an OGTT in 2003–2008 to a state-wide private pathology service (MP Services, Australia); the AusDiab population comes from a na-tional population-based study (2004–2005 AusDiab follow-up) (5). Only people with concurrent A1C and OGTT results are in-cluded here (MP group: n 2,494; Aus