Longitudinal Trajectories of HbA1c and Fasting Plasma Glucose Levels During the Development of Type 2 Diabetes

Abstract

OBJECTIVE To describe the trajectory of HbA1c and glucose concentrations before the diagnosis of diabetes. RESEARCH DESIGN AND METHODS The study comprised 1,722 nondiabetic Japanese individuals aged 26–80 years. Fasting plasma glucose (FPG) and HbA1c were measured annually for a mean of 9.5 (SD 1.8) years. RESULTS Diabetes occurred in 193 individuals (FPG ≥7.0 mmol/L, self-reported clinician-diagnosed diabetes, or HbA1c ≥6.5%). Mean HbA1c values were >5.6% each year before diagnosis in diabetes cases. Mean HbA1c (5.69% [95% CI 5.50–5.88]) was higher in the 21 individuals who developed diabetes 10 years after the baseline examination than in nondiabetic individuals after 10 years (5.27% [5.25–5.28]). From 3 years to 1 year prediagnosis, HbA1c increased 0.09% (SE 0.01)/year, reaching 5.90% (5.84–5.96) 1 year prediagnosis. In the entire group, marked increases in HbA1c of 0.3% (SE 0.05%)/year and FPG of 0.63 (0.07) mmol/L/year predicted diabetes. CONCLUSIONS HbA1c trajectory increased sharply after gradual long-term increases in diabetic individuals.