Hemoglobin within normal range is negatively related to hemoglobin A1c in a nondiabetic American population aged 16 years and older

BACKGROUND Protein glycosylated hemoglobin,hemoglobin A1c(HbA1c)binds hemoglobin(Hb)in red blood cells to blood glucose.However,the relationship between Hb and HbA1c remains unclear.AIM To elucidate their relationship in a nondiabetic population aged≥16 years in the United States,using data from the 1999-2018 National Health and Nutrition Examination Survey.METHODS This study was based on data from 44560 adults aged≥16 years,excluding those with diabetes.The relationship was estimated using a multivariate regression.We also used piecewise linear regression for subgroup analysis based on age and sex stratification and analysis of the threshold effects of Hb on HbA1c.RESULTS Hb and HbA1c levels were negatively correlated in the unadjusted model(β=-0.01;95%CI:-0.01,-0.01).The correlation was significantly negative when the regression model was minimally regulated and stratified by age and sex,and remained negative when the model was further regulated(more than 10%)to identify covariates with the HbA1c level influence estimates.In subgroup analyses based on age and sex stratification,the association remained negative when the covariates were controlled.A nonlinear relationship was observed between them when the Hb levels reached the tipping point(13.2 g/dL)(adjusted odds ratio,-0.04;95%CI:-0.05,-0.03)and when the Hb levels exceeded 13.2 g/dL(adjusted odds ratio,-0.10;95%CI:-0.10,-0.09).CONCLUSION Our study shows that normal Hb levels are negatively correlated with HbA1c in nondiabetic Americans aged≥16 years.