Diagnostic ability of elevated 1-h glucose challenge test

Objective: To determine whether a threshold of a 1-h glucose challenge test (GCT) eliminates the need for a 3-h glucose tolerance test (GTT). Study Design: A retrospective cohort of patients undergoing GTT after GCT was ⩾140 mg dl −1 . Gestational diabetes mellitus (GDM) was diagnosed using National Diabetes Data Group (NDDG) and Carpenter–Coustan (CC) criteria. Sensitivity, specificity and predictive values were calculated for 1-h GCT values of 160 to 220 mg dl −1 . Result: Of 6218 patients, 988 (15.9%) had an elevated GCT and 753 (12.1%) underwent a GTT. In all, 165 (2.7%) were diagnosed with GDM using NDDG criteria, and 250 (4.0%) by CC criteria. The positive predictive value of a 1-h of GCT ⩾200 mg dl −1 for GDM was 68.6% by NDDG and 80.0% for GDM by CC criteria. Conclusion: Although the predictive value of an elevated 1-h ⩽200 mg dl −1 for GDM was high, 1 in 3 to 1 in 5 women would be overdiagnosed with GDM if the 3-h GTT was omitted.