Random plasma glucose and the glucose challenge test in pregnancy

The oral glucose tolerance test for detecting women with gestational diabetes is too complicated and prolonged for routine use. Similar and less time consuming screening tests have been proposed including random plasma glucose estimation and the glucose challenge test (blood glucose estimation one hour after a 50 g glucose load). However, in practice, correct timing of the blood sample, which is of critical importance in the interpretation of the results of these tests, is difficult to ensure. This study was designed to evaluate these two screening tests in identifying women with abnormal glucose tolerance in pregnancy.

One hundred and eleven consecutive pregnant women at risk for gestational diabetes and 121 consecutive pregnant women with no risk factors had random plasma glucose estimation followed by the 50 g glucose challenge test at 26 to 30 weeks of gestation. A 100 g 3 hour oral glucose tolerance test was done within two weeks of the screening tests. The sensitivity and specificity of screening tests in predicting abnormal glucose tolerance were calculated.

Seven (6.3%) women in the high risk group and four (3.3%) in the low risk group had gestational diabetes, while 11 (9.9%) and 8 (6.6%) had impaired glucose tolerance. Random plasma glucose level of 90 mg/dl or greater had a sensitivity of 63% and specificity of 66% in predicting abnormal glucose tolerance, while a threshold level of 115 mg/dl for the glucose challenge test yielded a sensitivity of 63% and a specificity of 55%.

Neither random plasma glucose estimation nor the glucose challenge test is a useful screening procedure for abnormal glucose tolerance in pregnancy.