HbA1c as a diagnostic tool for diabetes

The recommendations for the diagnosis of diabetes are based on fasting glucose, and also the 2-h glucose following a 75-g oral glucose tolerance test. A third glycaemic marker, HbA1c, has been discussed but not proposed because of assay standardisation problems. All three markers are predictive of microvascular and macrovascular complications of diabetes, as well as the incidence of diabetes. Further, the intraindividual variability of HbA1c should be better than either fasting or 2-h glucose because it is an integration of glucose levels over a period of 1-2 months; however, the existing studies on its biological variability are not definitive. These three criteria do not define the same groups of subjects, and we need to know more about the incidence of morbidity and mortality associated with each of these criteria, especially in those subjects who have high values for only one or two of these measures. (C) 2003 Elsevier B.V. All rights reserved.