Meaning of upper limit of normal range of post‐load 1‐h plasma glucose level defined by oral glucose tolerance test in Japanese subjects

AIMS/INTRODUCTION: To identify upper limit post‐load 1‐h plasma glucose (1‐h PG) after 75‐g oral glucose test in a Japanese population. MATERIALS AND METHODS: A total of 918 subjects were enrolled. We divided the subjects into two groups: normal 2‐h post‐load plasma glucose (2‐h PG; <140 mg/dL) and impaired 2‐h PG group (≥140 mg/dL). RESULTS: A total of 417 subjects had normal 2‐h PG and 501 had impaired 2‐h PG. The receiver operating characteristic (ROC) curve showed that the optimal cut‐off value of 1‐h PG was 179 mg/dL (area under ROC curve = 0.89), providing that the sensitivity, specificity, and positive and negative predictive value were 85, 79, 82 and 83%, respectively. The subjects with 1‐h PG < 179 mg/dL consisted of 0.5% diabetes and 99.5% non‐diabetes, whereas those with 1‐h PG ≥ 179 mg/dL consisted of 26.9% diabetes and 73.1% non‐diabetes (P < 0.01). Furthermore, there was a significant correlation between 1‐h PG and 2‐h PG (r(2) = 0.57, P < 0.01). CONCLUSIONS: These data suggested that 179 mg/dL is the upper limit of the normal range of post‐load of 1‐h PG in a Japanese population. Thus, the subjects with 1‐h PG ≥ 179 mg/dL might be at risk of developing future diabetes. Therefore, appropriate prospective study should be carried out to test this hypothesis.