One-Hour Postload Glucose Is a More Sensitive Marker of Impaired β-Cell Function Than Two-Hour Postload Glucose

There is evidence that 1-h plasma glucose (PG) concentration during the 75-g oral glucose tolerance test (OGTT) is superior to 2-h PG level in predicting diabetes. We investigated the characteristics of insulin sensitivity and β-cell function behind this observation. After age, sex, and BMI matching, 496 study participants selected from 3,965 individuals without diabetes who were at high risk of type 2 diabetes in a tertiary medical center were categorized into four groups in a 1:1:1:1 ratio based on OGTT results: 1) 1-h PG level <8.6 mmol/L and 2-h PG level <7.8 mmol/L (normal glucose tolerance [NGT]/1h-normal); 2) 1-h PG level ≥8.6 mmol/L and 2-h level <7.8 mmol/L (NGT/1h-high); 3) 1-h PG level <8.6 mmol/L and 2-h level ≥7.8 mmol/L (impaired glucose tolerance [IGT]/1h-normal); and 4) 1 h PG level ≥8.6 mmol/L and 2-h level ≥7.8 mmol/L. Compared with participants with IGT/1h-normal, those with NGT/1h-high had a similar extent of insulin resistance but lower early-phase insulin secretion. Additionally, participants with NGT/1h-high had a lower disposition index at both 0-30 min and 0-120 min than those with IGT/1h-normal. The fitted regression line relating PG to log-transformed disposition index (0-30 min and 0-120 min) was significantly steeper for 1-h than 2-h PG. In conclusion, 1-h PG seemed to be more sensitive to the deterioration in β-cell function than was 2-h PG. The use of 1-h PG may identify individuals at high risk of type 2 diabetes at an earlier stage.