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)

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.Trajectories of plasma glucose concentrations, insulin resistance, and insulin secretion to reflect the pathogenesis of type 2 diabetes were studied (1–8). Although HbA_1c is used to diagnose diabetes or indicate a prediabetic state in some countries (9), the long-term trajectory of HbA_1c before diabetes is little known. We retrospectively examined 10-year longitudinal data on apparently healthy Japanese individuals to investigate prediabetic changes in HbA_1c and compare such changes with those of fasting plasma glucose (FPG).