A 50-G Glucose Challenge Test: Is There Any Diagnostic Cut-Off?
Waralak Yamasmit MD*, Surasith Chaithongwongwatthana MD, MSc**, Boonchai Uerpairojkit MD**
Affiliation : * Department of Obstetrics and Gynecology, Bangkok Metropolitan Administration (BMA) Medical College and Vajira Hospital, Bangkok ** Department of Obstetrics and Gynecology, Faculty of Medicine, Chulalongkorn University, Bangkok
Objective : To evaluate the diagnostic performance of 50-g glucose challenge test for diagnosis of gestational
diabetes.
Material and Method: A retrospective study was conducted by reviewing the medical records of pregnant
women who had a 50-g glucose challenge test of 140 mg/dL or higher and followed by a 100-g glucose
tolerance test. Results were categorized in 10 mg/dL increments. Gestational diabetes was diagnosed using
National Diabetes Data Group criteria.
Results : The present study included 2,226 cases from universal screening of 11,084 pregnant women. The
incidence of gestational diabetes was 3.2% (351/11,084). Only 1.6% (6/374) of patients with positive screening
results of less than 145 mg/dL had gestational diabetes. All of the 6 women undiagnosed by this threshold were
gestational diabetes class A1 and had at least one risk factor. Of 1,875 women, seven cases (0.4%) would be
over diagnosed as gestational diabetes if 100-g glucose tolerance test was not performed after a result of 50-
g glucose challenge test of > 250 mg/dL (99.6% specificity, 85.8% negative predictive value, 12.3% sensitivity
and 86.0% positive predictive value).
Conclusion : A 50-g glucose challenge test may be used as a diagnostic test when the value is > 250 mg/dL. The
present data suggested that the value of glucose screening of > 145 mg/dL can be used as a threshold for a
positive test in the low risk women.
Keywords : Gestational diabetes, Glucose challenge test, Glucose tolerance test, Diagnostic test
