COMPARISON OF TESTS FOR GLYCATED HEMOGLOBIN AND FASTING AND 2 HOUR PLASMA-GLUCOSE CONCENTRATIONS AS DIAGNOSTIC METHODS FOR DIABETES

Objective-To compare the ability of tests measuring two hour plasma glucose, fasting plasma glucose, and glycated haemoglobin concentrations in predicting the specific microvascular complications of non-insulin dependent diabetes mellitus. Design-Cross sectional and longitudinal analysis of the relation between complications and concomitant results of the three tests. Setting-Gila River Indian Community, Arizona. Subjects-Pima Indians (cross sectional, n=960), aged 25 years or above who were not receiving insulin or oral hypoglycaemic treatment at the baseline examination. Main outcome measures-Developement of retinopathy and nephropathy. Results-Cross sectionally, frequency distributions of logarithms of the three sets of results were bimodal, with the prevalence of retinopathy and nephropathy being, respectively, 12.0-26.7 and 3.9-4.2 times as high above as below cut off points which minimised overlap (two hour plasma glucose concentration 12.6mmol/l; fasting plasma glucose concentration 9.3mmol/l; glycated haemoglobin (HbA(1c)) concentration 7.8%). Longitudinally, each of the three measures of glycaemia significantly predicted the development of retinopathy (P<0.0001) and nephropathy (P<0.05). Receiver operating characteristic curves showed that two hour plasma glucose concentration was superior to fasting plasma glucose concentration (P<0.05) for prevalent cases of retinopathy, but otherwise no variable had a significant advantage for detecting incident or prevalent cases of either complication. Conclusions-These findings suggest that determination of glycated haemoglobin or fasting plasma glucose concentrations alone may be acceptable alternatives to measuring glucose concentration two hours after challenge with 75g glucose for the diagnosis of diabetes.