Importance of OGTT for diagnosing diabetes mellitus based on prevalence and incidence of retinopathy

Study was made on the necessity and importance of the oral glucose tolerance test (OGTT) for diagnosing diabetes mellitus based on prevalence and incidence of diabetic retinopathy. Subjects were 12 208 persons undergoing OGTT between 1965 and 1997. The prevalence of retinopathy was significantly elevated with FPG greater than or equal to 126 and 2-h PG greater than or equal to 198 mg/dl. The incidence of retinopathy was 15-30/10 000 person-years (PY) with FPG < 125, but with FPG of 126-139 it was significantly higher (69/10 000 PY) and at 140-199 mg/dl it was elevated to 139/10 000 PY. Subjects were classified at initial test into FPG < 110, 110 125, 126-139, and greater than or equal to 140 and further into 2-h PG < 200 and greater than or equal to 200 mg/dl for comparison with the incidence of retinopathy. Even with the same FPG, the incidence was two- to threefold higher with 2-h PG greater than or equal to 200 mg/dl, indicating that 2-h PG was highly associated with the incidence of retinopathy. As for IFG, the prevalence of diabetes as defined by 2-h PG greater than or equal to 200 in the OGTT increased with elevated FPG, and 33.7% of IFG cases showed 3-h PG greater than or equal to 200 mg/dl. Based on the prevalence and incidence of retinopathy, we conclude that 126 mg/dl FPG is an appropriate cut-off level, and the OGTT is important for diagnosing mild diabetes mellitus. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.