Glucose challenge test-Is it an effective screening tool for gestational diabetes mellitus in low risk population?

Objective: To evaluate the validity of 50 g oral Glucose challenge test (GCT) as a screening tool for gestational diabetes mellitus (GDM) in terms of its sensitivity, specificity, positive predictive value and negative predictive value in our population. Methodology: This cross sectional comparative study was conducted at the Department of Gynecology and Obstetrics, Shalamar Hospital, Lahore, Pakistan from July 2006 to June 2007. It included 100 women carrying singleton pregnancy with 20-35 years of age booked in first trimester. Patients with risk factor of GDM or with established type DM were excluded from study. After informed consent, 50g GCT was done between 24-28 weeks of gestation. Venous plasma glucose level was measured after 1 hour of glucose load using 140 mg/dl as a cut off value. Regardless of results of screening, all patients were tested with 100 g oral glucose tolerance test (OGTT) as "gold standard" of diagnosis of GDM. Validity of 50g GCT was calculated in term of sensitivity, specificity, positive predictive value and negative predictive value. Data were analysed using SPSS v. 16. Results: Out of 100 patients, 19% were positive and 81 % negative on 50g GCT. With 1 Og OGTT, true positive were 10 out of 19(52.6%) positive, and false positive were 9 out of 19(47.4%) positive. False negative were 3 out of 81(3.7%) negative, whereas true negative were 78 out of 81(96.3%) negative. 50g GCT had sensitivity of 76.92%, specificity of 89.6%, positive predictive value of 52.6% and negative predictive value of 96.2%. Conclusion: 50g GCT was an effective screening tool for GDM when applied to our population between 24-28 weeks of gestation with adequate sensitivity and specificity. (Rawal Med J 2014; 39: 428-431).