Is random plasma glucose an efficient screening test for abnormal glucose tolerance in pregnancy?

Random plasma glucose was determined in 276 apparently healthy pregnant women attending our antenatal clinic at 28 to 32 weeks gestation. Mean and standard deviation values within 2 h and greater than 2 h after a meal were calculated. A standard 75-g oral glucose tolerance test was then given to 250 of the 276 pregnant women. Three patients were found to be diabetic and 46 had post-load concentrations indicative of impaired glucose tolerance according to the criteria of the World Health Organization (1980). Using a cut-off point whereby 15% of the population would be tested, we would have identified only 2 of the 3 diabetics and 12 of the 46 with impaired glucose tolerance. This poor predictive power cannot be resolved by altering cut-off points for screening, or by altering the criteria for abnormal glucose tolerance. The basic problem is lack of a close relation between 2-h glucose tolerance value and random glucose when this has been taken greater than 120 min after a meal. In this population with a high prevalence of abnormal glucose tolerance, random plasma glucose is not an efficient screening test.