Longitudinal trajectories of HbA1c and fasting plasma glucose levels during the development of type 2 diabetes: the Toranomon Hospital Health Management Center Study 7 (TOPICS 7)

Abstract

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.

Figure 1

Trajectory of values for FPG (A), HbA_1c (B) (●, individuals who developed diabetes; ○, individuals who did not develop diabetes), and differences in FPG and HbA_1c values between cases and noncases (C) before the diagnosis of type 2 diabetes. Data in the boxes show annual increases in FPG or HbA_1c values during –5 to –3, –3 to –1, or –1 to 0 years before the diagnosis of diabetes. Slope difference vs. nondiabetic individuals: **P < 0.001, *P < 0.01. The value for HbA_1c (%) was estimated as the NGSP equivalent value (%) calculated by the formula [HbA_1c (%) = HbA_1c (Japan Diabetes Society) (%) + 0.4%].