Relationship between Time in Range Derived from Flash Glucose Monitoring System and HbA1c

Objective To explore the relationship between time in range (TIR) derived from flash glucose monitoring system (FGM) and HbA1c in Chinese adults with type 1 diabetes mellitus (T1DM). Methods Adult T1DM patients attended outpatient department of Peking Union Medical College Hospital (PUMCH) between October 2018 to March 2019 were included. HbA1c and data of FGM were obtained at the same time. TIR was calculated, and the relationship between TIR and HbA1c was investigated by correlation and regression analysis. Results A total number of 77 patients who met the inclusion and exclusion criteria were included in the analysis. The average HbA1c was (7.5±1.3)%; TIR 62.0 (48.7, 67.8)% and CV (coefficient of variation) (39.7±8.1)%. TIR derived from FGM had a negative liner correlation with HbA1c (r=-0.645, P<0.001). The regression equation is:HbA1c=10.58-0.05×TIR. The HbA1c level decreased by 0.5% for every 10% increase in TIR. TIR was correlated with HbA1c negatively in both patients with stable glucose (CV<36%) and unstable glucose (CV ≥ 36%), but the correlation coefficient between TIR and HbA1c in stable glucose patients was higher. For a specific TIR, HbA1c was higher in stable glucose patients. Conclusions The FGM-derived TIR could be helpful in the glucose management of Chinese adult T1DM, while glucose variability should be taken into consideration in interpreting the relationship between TIR and HbA1c.