Cut-off values of fasting and post-load plasma glucose and HbA _1c for predicting Type2 diabetes in community-dwelling Japanese subjects: The Hisayama Study

Aims We examined the optimal cut-off values of fasting plasma glucose, 2-h post-load glucose and HbA _1c for predicting Type2 diabetes in community-dwelling Japanese subjects. Methods A total of 1982 subjects without diabetes aged 40-79years who underwent a 75-g oral glucose tolerance test were followed prospectively for 14years by annual health examination. Results During the follow-up, 295 subjects developed Type2 diabetes. Compared with the first decile, the crude hazard ratio for incident Type2 diabetes was significantly higher in the fifth fasting plasma glucose decile [5.4-5.4mmol/l (97-98mg/dl)] or higher, in the seventh 2-h post-load glucose decile [6.9-7.2mmol/l (124-131mg/dl)] or higher, and in the fifth HbA _1c decile [34-36 mmol/mol (5.3-5.4%)] or higher. These associations remained substantially unchanged even after adjustment for confounding factors. The receiver operating characteristic curve analysis showed that the optimal cut-off values for predicting Type2 diabetes were 5.6mmol/l (101mg/dl) for fasting plasma glucose, 6.9mmol/l (124mg/dl) for 2-h post-load glucose and 37mmol/mol (5.5%) for HbA _1c. In a stratified analysis, the cut-off values were approximately 5.6mmol/l (101mg/dl) for fasting plasma glucose and 37mmol/mol (5.5%) for HbA _1c, and these values were unchanged over BMI quartile levels, whereas the 2-h post-load glucose cut-off values declined with decreasing BMI levels. Conclusions Our findings suggest that the cut-off value for predicting Type2 diabetes in the Japanese population is 5.6mmol/l (101mg/dl) for fasting plasma glucose and 37mmol/mol (5.5%) for HbA _1c, while the 2-h post-load glucose cut-off value is lower than the diagnostic criterion for impaired glucose tolerance.