Limitation of Fasting Plasma Glucose for the Diagnosis of Diabetes Mellitus

We have analyzed data from 3370 OGTTs performed during epidemiologic studies in three different ethnic groups (Micronesian, Polynesian, and Melanesian) in various Pacific countries to examine the value of a single fasting plasma glucose greater than or equal to 140 mg/dl as a diagnostic test for diabetes (defined as 2-h plasma glucose greater than or equal to 200 mg/dl). A fasting plasma glucose greater than or equal to 140 mg/dl is a highly specific test for diabetes, specificity in the various populations ranging from 98.1% to 99.7%. On the other hand, the sensitivity of fasting plasma glucose was not high and varied greatly between the populations (46.2%-79.0%). The predictive value of fasting plasma glucose for the diagnosis of diabetes was lowest in populations with a low diabetes prevalence and improved in higher prevalence groups. These data indicate that a fasting plasma glucose greater than or equal to 140 mg/dl is not a good screening test, apart from populations with a high prevalence of diabetes mellitus, and the 2-h postload plasma glucose is preferable.