Characteristics of the glycometabolic categories based on the oral glucose tolerance test results in Japanese adults without diabetes

OBJECTIVE: We aimed to classify Japanese adults without diabetes into different categories based on the oral glucose tolerance test (OGTT) and characterize their insulin sensitivity and insulin secretion. PATIENTS AND METHODS: The OGTT was performed on 1,085 Japanese individuals without diabetes (aged 20–64 years); blood glucose and insulin levels were measured at 0, 30-, 60-, 90-, and 120-min. Fasting blood chemistry, hematology, and urine were analyzed. The participants were classified into four categories based on the following: (A) 30 min post-load plasma glucose levels < 157 mg/dL and/or (B) 120 min post-load plasma glucose levels < 126 mg/ dL and Matsuda index > 4.97. Category 1 satisfied both conditions, category 2 satisfied condition A but not B, category 3 satisfied condition B but not A, and category 4 satisfied neither condition. RESULTS: Overall, 46%, 21%, 13%, and 20% of the participants were classified into categories 1, 2, 3, and 4, respectively. Compared with category 1, the characteristics of the other categories were: 2, low insulin sensitivity and high blood glucose levels during the later period; 3, low insulin secretion and a rapid increase in blood glucose levels; and 4, combined characteristics of categories 2 and 3. Most blood test values besides glucose metabolism in category 4 were also worse than those in category 1. Categories 1 and 2 had a high proportion of females, whereas categories 3 and 4 had a low proportion. CONCLUSIONS: Japanese adults without diabetes are classified into four categories with different insulin sensitivities and insulin secretion using OGTT results. Each category has different characteristics of age and sex distribution and clinical values besides glucose metabolism.