Objective. We examined the relationship between fasting plasma glucose (FPG) and 2-hour postload glucose (2-h PG) levels, and the optimal FPG cut-off level to correspond to a 2-h PG of 11.1 mmol/l, the gold-standard diagnostic criterion, in a general Japanese population.

Design. Cross-sectional study populations of 2,421 subjects in 1988 and 2,698 subjects in 2002, aged 40 to 79 years and without antidiabetic medication, were tested with an OGTT. The relationship between FPG and 2-h PG was investigated by various regression models and a receiver operating characteristic (ROC) curve.

Results. The best-fit model for the relationship between FPG and 2-h PG was a quadratic regression model. The FPG cut-off levels corresponding to the 2-h PG of 11.1 mmol/l by this model were 6.2 mmol/l in 1988 and 6.3 mmol/l in 2002. In the combined populations, the FPG cut-off point was 6.3 mmol/l; the sensitivity and specificity of this cut-off point for detecting a 2-h PG of 11.1 mmol/l were 75.2% and 88.6%, respectively. The ROC curve analysis confirmed that the corresponding FPG point was 6.2 mmol/l in both the 1988 and 2002 populations. In a stratified analysis, the FPG cut-off level increased with increasing BMI levels; however, even in subjects with BMI 30 kg/m², the FPG cut-off level was lower than 7.0 mmol/l.

Conclusions. Our findings suggest that the FPG cut-off level corresponding to the 2-h PG of 11.1 mmol/l in the general Japanese population is lower than the current diagnostic criterion.