Investigation on translating glycated hemoglobin A1c into mean blood glucose in Chinese subjects

Abstract

Objective To establish the corresponding value of mean blood glucose (MBG) for a specific target of glycated hemoglobin A1C (HbA1c), and evaluate the relationship between 24 hour MBG determined by continuous glucose monitoring and HbA1c in subjects with different states of glucose tolerance. Methods From August 2007 to January 2010, 318 subjects who accepted oral glucose tolerance test in out-patient department and ward of Shanghai Jiao Tong University Affiliated Sixth People's Hospital were enrolled, including 115 with normal glucose regulation, 57 with impaired glucose regulation and 146 with newly diagnosed type 2 diabetes. Based on the diagnostic criteria specified in American Diabetes Association (ADA, 2003) guidelines, categories of glucose tolerance were defined as diabetes mellitus and impaired glucose regulation.Biochemical indicators were investigated in each group. Oral glucose tolerance test was performed and 2-h postchallenge glycemia (2 h PG) was also measured. MBG was measured with continuous glucose monitoring system. HbA1c was measured with high performance liquid chromatography method. The correlations among MBG, HbA1c and the other parameters monitored were analyzed. Statistical analysis was performed using one way ANOVA, Kruskal-Wallis test, Chi-square test, Spearman correlation analysis and Linear regression analysis. Results (1)The levels of HbA1c and MBG in 318 subjects were (6.6±1.5)% and (7.3±2.3) mmol/L, respectively.(2)MBG was significantly correlated with HbA1c (r=0.848, P<0.01). Linear regression analysis, using MBG and HbA1c summarized by patient (n=318), produced a relationship of MBG=1.252×HbA1c-0.992 (R2=0.718, P<0.01). That is, MBG will increase 1.252 mmol/L with 1% increase of HbA1c. When HbA1c level was 6.5%, the expected value of MBG was 7.1 mmol/L. When HbA1c level was 7.0%, the expected value of MBG was 7.8 mmol/L.(3)In 146 patients newly diagnosed type 2 diabetes, the relationship between MBG and HbA1c was similar to that in total subjects (r=0.788, P<0.01), and the linear regression analysis showed a relationship of MBG=1.255×HbA1c-0.886 (R2=0.621, P<0.01). When HbA1c level was 6.5%, the expected value of MBG was 7.3 mmol/L. When HbA1c level was 7.0%, the expected value of MBG was 7.9 mmol/L. Conclusion We initially establish the corresponding value of MBG for a specific HbA1c target and provide the basis for translating HbA1c into mean blood glucose in Chinese subjects. Key words: Diabetes mellitus, type 2; Glycated hemoglobin A, glycosylated; Mean blood glucose; Continuous glucose monitoring