Hemoglobin A_1c as a marker for identifying diabetes and cardiovascular risk factors: the China Health and Nutrition Survey 2009

Hemoglobin A_1c (HbA_1c) has been recommended as an optional method for diagnosing diabetes. The impact of HbA_1c on the diagnosis of diabetes has not been evaluated in China, a country with the greatest number of people with diabetes in the world. Hence, we aim to examine how well HbA_1c performs as compared with fasting plasma glucose (FPG) for diagnosing diabetes in Chinese population. We conducted a cross-sectional analysis of 7,641 Chinese men and women aged ≥18 years using data from the China Health and Nutrition Survey 2009 in which FPG and standardized HbA_1c were measured. HbA_1c was measured with high-performance liquid chromatography system. Diabetes is defined as having FPG ≥7 mmol/l or HbA_1c ≥6.5 %. Overall, 5.0 and 5.8 % had undiagnosed diabetes by FPG ≥7 mmol/l and HbA_1c ≥6.5 %, respectively. Overlap between HbA_1c- and FPG-based diagnosis of diabetes was limited (n = 214, 34.9 %). Similar trends were noted in both genders, all age groups, urban/rural settings, regions, body mass index (BMI) categories, waist circumference (WC) groups, and blood pressure status. Solely HbA_1c-defined individuals exhibited higher levels of BMI, WC, total cholesterol, and hypersensitive C-reactive protein and lower levels of homeostasis model assessment of insulin resistance. We note limited overlap between FPG- and HbA_1c-based diagnosis of diabetes. The limited overlap between FPG- and HbA_1c-based diagnosis of diabetes persisted in each evaluated subgroup. HbA_1c criterion for the diagnosis of diabetes identifies individuals with a worse cardiovascular risk profile compared with FPG.