Rethinking the accuracy of 75 g glucose used in the oral glucose tolerance test in the diagnosis and management of diabetes

Aims We investigated the specificity of the 75 g oral glucose tolerance test (OGTT) and the clinical usefulness of the 2 h post loading glucose (2 h PLG) value in the clinical care of diabetes patients. Methods The 75 g OGTT data of 1755 subjects were analyzed. The relationships and degrees of consistency among 2 h PLG, fasting plasma glucose (FPG), and HbA1c values were assessed. We also investigated the degree of contribution of 2 h PLG in the prescription of glucose-lowering agents and in the pitfall group for use of 75 g OGTT. Results Among 595 subjects with normal FPG, only 329 (55.3%) showed normal 2 h PLG level, and 66 (11.1%) patients could be considered as having diabetes. Among 454 diabetes patients (based on FPG and HbA1c), 409(90.1%) showed 2 h PLG values in the range of diabetes, 45 (9.9%) subjects did not exhibit diabetes. Pitfall group who used 75 g OGTT for diagnosis diabetes (lower 2 h PLG value compared to fasting and upper 2 h PLG value compared to fasting) showed differences in body weight and height. Conclusions Based on OGTT results, around 10% patients cannot be diagnosed with diabetes based solely on the 2 h PLG value. Further studies on differences in glucose loading according to body weight, individual life pattern, and calorie requirement are needed for improvement of the specificity of the OGTT in the clinical management of diabetes.