Effect of age and race/ethnicity on HbA1c levels in people without known diabetes mellitus: Implications for the diagnosis of diabetes

Aims: To determine if age and race/ethnicity affect HbA1c levels independent of glycemia. Methods: We analyzed 2712 individuals from the NHANES III population 40-74 years old without diabetes history. Results: HbA1c levels increased by 0.10% per decade in people with NGT and 0.07% in those with IFG and/or IGT, independent of fasting and 2-h glucose on OGTT's. Compared to nonHispanic whites, HbA1c levels increased by 0.12% (NGT) and 0.10% (IFG/IGT) in Mexican-Americans and 0.21% (NGT) and 0.35% (IFG/IGT) in non-Hispanic blacks, independent of glycemia. At HbA1c levels of >= 6.5%, >= 7.0% and 6.5-6.9%, diabetes diagnosed by current FPG/OGTT criteria occurred in 82%, 94% and 65%, respectively. In non-Hispanic blacks with HbA1c levels of 6.5-6.9%, 68% of those 40-74 years old and 87% of those over 64 years old would not have diabetes by FPG/OGTT criteria. Over 90% of all race/ethnicity groups would have diabetes with HbA1c levels >= 7.0%. Conclusions: Because many people, especially older non-Hispanic blacks, with HbA1c levels of 6.5-6.9% would not have diabetes by current FPG/OGTT criteria and clinical retinopathy and nephropathy are very unusual in patients whose HbA1c levels are kept <7.0%; we recommend an HbA1c level of >= 7.0% to diagnose diabetes. (C) 2009 Elsevier Ireland Ltd. All rights reserved.