Longitudinal Trajectories of HbA(1c) and Fasting Plasma Glucose Levels During the Development of Type 2 Diabetes: The Toranomon Hospital Health Management Center Study 7 (TOPICS 7)

OBJECTIVE: To describe the trajectory of HbA(1c) 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 HbA(1c) 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 HbA(1c) ≥6.5%). Mean HbA(1c) values were >5.6% each year before diagnosis in diabetes cases. Mean HbA(1c) (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, HbA(1c) increased 0.09% (SE 0.01)/year, reaching 5.90% (5.84–5.96) 1 year prediagnosis. In the entire group, marked increases in HbA(1c) of 0.3% (SE 0.05%)/year and FPG of 0.63 (0.07) mmol/L/year predicted diabetes. CONCLUSIONS: HbA(1c) trajectory increased sharply after gradual long-term increases in diabetic individuals.