Diagnosing Diabetes With Glucose Criteria: Worshipping a False God

Abstract

In this issue of Diabetes Care , Dr. David Sacks has nicely delineated the pros and cons of the measurements of glucose concentrations and A1C levels and the resulting effects on using each to diagnose diabetes (1). With the continued improvement in A1C assays, the balance seems to increasingly favor using A1C levels. This commentary will examine an issue that has received scant attention in the past, i.e., what is the actual evidence upon which the current glucose criteria for diagnosing diabetes mellitus is based? Glucose concentrations in almost all populations (except those with very high prevalences of diabetes, e,g., Pima Indians), are distributed unimodally with a rightward skew (2,3), making the choice of a diagnostic value for diabetes arbitrary. If glucose concentrations are log-transformed to minimize the rightward skewness, a bimodal distribution has been noted (4–8). However, cutoff values defining the two distributions have ranged from 200–307 mg/dL, mostly depending on the ages of the population surveyed (3–8). Prior to 1979, at least six different sets of criteria diagnosed diabetes (9). In 1979, the National Diabetes Data Group (NDDG) resolved this issue by establishing one set of criteria (10). They selected these criteria based on glucose concentrations that allegedly predicted the development of diabetic retinopathy, a specific microvascular complication of diabetes. Three prospective studies (11–13) were available to the NDDG on which to base their decision. A total of 1,213 patients were followed for 3 to 8 years after oral glucose tolerance tests (OGTTs), 77 of whom developed retinopathy. There was no further evaluation of their glycemic status after the original OGTT, although it was very likely that the 77 people who developed retinopathy in the studies used by the NDDG to establish the diagnostic criteria had increasing glycemia in …