Fasting plasma glucose reference values among young Japanese women requiring 75g oral glucose tolerance tests.

Objective: Currently there are various discussions on the upper limit of FPG (Fasting Plasma Glucose) levels. In Japan, when abnormal levels of FPG are detected at general health checkups or complete physical examinations, 75g Oral Glucose Tolerance Tests (75g OGTT) are often conducted in follow-up examinations. Therefore we investigated the appropriate upper limit of FPG levels to decide whether 75g OGTT are actually necessary.

Research Design And Methods: Based on the FPG levels of 256,309 women with an age range of 20 to 79, we established the upper limits of FPG levels by 5-year intervals, using a method equivalent to the National Committee for Clinical Laboratory Standards (NCCLS) used in the U. S. [4]. We also obtained the ROC curve from the 75g OGTT results from 160 women aged 20 to 39. We then divided those 160 women into four categories based on their 75g OGTT results, and compared the abnormal rates of their 2-hour post-75g OGTT glucose levels, HOMA-R and Insulin Index using the Kruskal-Wallis test.

Results: The upper limits of FPG levels were 99 mg/dl in the 20-29 age range, 101 mg/dl in the 30-34 age range, and 104 mg/dl in the 35-39 age range. The upper limits of the FPG reference intervals increased almost proportionally up to the age 50, and showed little difference thereafter. The point on the ROC curve where the total value of sensitivity plus specificity reached the highest had an FPG level of 99.5 mg/dl. For 2-hour post-75g OGTT glucose levels and HOMA-R, there was a significant difference in abnormal rates between the categories of FPG ≤ 99 mg/dl and 100 ≤ FPG ≤ 109 mg/dl, but not in Insulin Index.

Conclusions: We believe that 75g OGTT are necessary for Japanese women aged 20 to 39 with FPG levels of 100 mg/dl or above.