The study on the normal ranges and related factors for glycated hemoglobin in 9 711 persons with normal glucose tolerance

Objective To analyze the result of glycated hemoglobin (HbA1c) measurement and related factors in persons with normal glucose tolerance (NGT). Methods A 75 g glucose tolerance test (OGTT) was conducted in all participants from diabetes screening population of Shougang four communities. HbA1c, fasting plasma glucose (FPG), 2 hour plasma glucose (2 hPG) after OGTT and blood biochemical tests were conducted. Anthropometric measurements were performed to all the subjects. A total of 9 711 individuals with normal FPG and 2 hPG were included for data analysis. All the subjects were divided into three groups by levels of HbA1c, and the clinical characteristics of the three groups were compared. Logistic regression was used to analyze the correlation of HbA1c to related factors. Results ① HbA1c was normally distributed in NGT populations. The range of HbA1c was 4.9%-6.5% (5.69±0.44)%. There was significant difference in HbA1c between men (5.68 ± 0.44)% and women (5.70 ± 0.44)% (P<0.05). Especially, there was significant difference (P<0.01) between the older group (60 to 79 years old) and the other grooups. ②HbA1c increased with age. There was significant differences among the young group (16 to 44 years old), middle-aged group (45-59 years), the elderly groups and very elderly group (≥80 years) in HbA1c, FPG and 2 hPG (P<0.01), whereas there was no significant difference between the elderly groups and the very elderly group. ③ There were statistically significant differences between HbA1c≤5.6% group and HbA1c 5.7%-6.4% group, HbA1c≥6.5% group in body mass index (BMI), waist-hip ratio (WHR), systolic blood pressure (SBP), serum total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL-C) levels, FPG and 2 hPG (P<001 or P<005), whereas there was no significant difference between HbA1c 5.7%-6.4% group and ≥the 6.5% group. ④ Logistic regression analysis showed that HbA1c was positively correlated with gender, age, BMI, WHR, SBP, TC, FPG, and was negatively correlated with DBP, HDL-C (OR: 1.377, 1.018, 1.033, 22.867, 1.011, 1.3, 4.049, 0.973, 0.835, respectively). Conclusion HbA1c is positively correlated with age and FPG in the population with normal glucose tolerance. The non-diabetic population with high risk HbA1c should undergo monitoring for FPG, 2 hPG and related cardiovascular risk factors. Key words: Glucose tolerance test; Age groups; Blood glucose; Glycated hemoglobin