Objective To investigate the optimal glycated haemoglobin (HbA1c) cut off points and evaluate the impact of HbA1c on diabetes and pre-diabetes in middle-aged and elderly population. Methods Subjects were recruited from Shanghai Changfeng Study. A total of 1 973 community-based participants (age≥45) without known diabetes underwent oral glucose tolerance test (OGTT) by using a 75-g oral glucose load and HbA1c was measured by using high performance liquid chromatography (HPLC). Subjects were classified as normal glucose tolerance (NGT), pre-diabetes(impaired glucose regulation, IGR) and new diagnosed diabetes (NDD) per 1999 WHO criteria. Two tests are compared with receiver operating characteristic curve (ROC). Results Among 1973 subjects, 271 (13.7%) were diagnosed as NDD and 474 (24.0%) as IGR by using OGTT. HbA1c was 5.7%±0.7% in this population. Use of 6.5% as the HbA1C cutoff point has sensitivity of 38.7% and specificity of 98.5%. We recommend 6.0% as a better cutoff value for diagnosis of diabetes in this population (AUC 0.829, 95% CI 0.798-0.860, P<0.001) with its sensitivity and specificity as 66.1% and 86.8%. For IGR, the results showed low sensitivity (44.9%) and specificity (66.7%) with an AUC of 0.571 for HbA1c when 5.8% was used as the cutoff point. Participants detected with HbA1c≥6.0% were associated with nearly the same metabolic characteristics, including body mass index (BMI), blood pressure, lipid profile and urine albumin-creatinine ratio (uACR) compared with diabetic subjects detected by OGTT. Conclusion The optimum HbA1c cutoff point for diabetes in our study population was lower than ADA criteria, and HbA1c may not be used to identify IGR. Objective To investigate the optimal glycated haemoglobin (HbA1c) cut off points and evaluate the impact of HbA1c on diabetes and pre-diabetes in middle-aged and elderly population. Methods Subjects were recruited from Shanghai Changfeng Study. A total of 1 973 community-based participants (age ≥45) without known diabetes underwent oral glucose tolerance test (OGTT) by using a 75-g oral glucose load and HbA1c was measured by using high performance liquid chromatography (HPLC). Subjects were classified as normal glucose tolerance (NGT) Results pre-diabetes (impaired glucose regulation, IGR) and new diagnosed diabetes (NDD) per 1999 WHO criteria. Two tests are compared with receiver operating characteristic curve (ROC). Results Among 1973 subjects, 271 (13.7%) were diagnosed as NDD HbA1c was 5.7% ± 0.7% in this population. Use of 6.5% as the HbA1C cutoff point has sensitivity of 38.7% and specificity of 98.5%. We recommend 6.0% as a better cutoff value for d The results showed low sensitivity (44.9%) and specificity (66.7%) for IGR, the results showed low sensitivity (44.9%) and specificity ) with an AUC of 0.571 for HbA1c when 5.8% was used as the cutoff point. Participants detected with HbA1c> 6.0% were associated with nearly the same metabolic characteristics, including body mass index (BMI), blood pressure, lipid profile and urine albumin -creatinine ratio (uACR) compared with diabetic subjects detected by OGTT. Conclusion The optimum HbA1c cutoff point for diabetes in our study population was lower than ADA criteria, and HbA1c may not be used to identify IGR.