Fasting Versus Postload Glucose Levels
Why the controversy?
- Hertzel C. Gerstein, MD, MSc
- Department of Medicine and the Division of Endocrinology and Metabolism, McMaster University, Hamilton, Ontario, Canada.
In 1997, the American Diabetes Association (ADA) published updated criteria for the diagnosis of diabetes and states of glucose tolerance (1). Its recommendation that the oral glucose tolerance test (OGTT) not be routinely used to identify people with either diabetes or impaired glucose tolerance (IGT) has fueled considerable controversy regarding the importance of such testing in either a clinical or epidemiological context (2,3,4,5,6,7,8,9). Generally, these reports have pointed out that a fasting plasma glucose (FPG) level alone will underestimate the prevalence of diabetes and/or underestimate the prevalence of IGT. Moreover, they have also pointed out that postload hyperglycemia is an early risk factor for cardiovascular (CV) events and that it may be a stronger predictor of CV events than fasting hyperglycemia (4). These observations have been cited to support a re-evaluation of the ADA recommendation and retention of the OGTT for routine use. However, a careful examination of the ADA recommendation suggests that this may in part be based on a misinterpretation of its underlying rationale. A brief review of some relevant data and of the significance of a diagnosis of diabetes and IGT may help to inform ongoing discussions regarding this issue.
Whither the diagnostic thresholds for diabetes and IGT?
In the ADA report of the expert committee, epidemiological data regarding the clinical significance of an OGTT were reviewed. In at least three different populations, a 2-h plasma glucose level ≥11.1 mmol/l (200 mg/dl) (measured after a 75-g oral glucose load) was a strong predictor of subsequent eye and kidney disease. Therefore, these data 1) confirmed that this 2-h glucose level was an appropriate cutoff in which to base a diagnosis of diabetes, 2) highlighted the fact that the …
