Diagnosing diabetes mellitus: Contemporary use of the oral glucose tolerance test in a regional diabetes centre

Following considerable debate on whether or not the oral glucose tolerance test (OGTT) should be retained, the revised WHO diagnostic criteria for diabetes recommended its continued use in certain defined circumstances. We have reviewed contemporary, use of the OGTT over 12 months in our regional diabetes centre. One hundred and eighty patients underwent an OGTT over a one-year period. The most common indication was fasting plasma glucose in the 5.5-6.9mmol/L range. Based on the OGTT and prior blood results, nine (5%) had normal carbohydrate tolerance, 40 (22%) had impaired fasting glucose, 52 (29%) had impaired glucose tolerance, and 53 (29.5%) satisfied the criteria for diabetes. Finally, 26 (14.5%) had, by this stage, only a single 'diagnostic' glucose value and required further testing. Twelve of these went on to have a second OGTT which confirmed diabetes in three and impaired glucose tolerance in nine. The remaining 14 had further fasting glucose estimations that confirmed diabetes in two cases, were normal in a further two and in the impaired fasting glucose range in 10. The test provided important information on the classification and diagnosis of diabetes. The OGTT continues to have a role in a selected group of patients with fasting blood glucose levels in the uncertain range. The need for a repeat OGTT is likely to increase as more asymptomatic patients are screened earlier in the evolution of glucose intolerance.