Gestational Diabetes Screen (ACOG Recommendations)

Serum or plasma

1 mL serum or plasma each tube

0.5 mL serum or plasma each tube

Gel-barrier tube or gray-top (sodium fluoride/potassium oxalate plasma) tube

None; glucose challenge is administered without regard to time of day or time of last meal.

Screening test for gestational diabetes

Enzymatic

70−139 mg/dL

The American College of Obstetricians and Gynecologists (ACOG) recommends that all pregnant women be screened for gestational diabetes mellitus (GDM)—whether by patient history, clinical risk factors, or with a 50-gram, one-hour loading test at 24 to 28 weeks of gestation to determine blood glucose levels—and suggests relying on the result of the 100-gram, three-hour oral glucose tolerance test for diagnosis (often referred to as a "two-step" method).²

The American Diabetes Association (ADA)³ released standards that vary from the ACOG recommendations. The ADA recommends a simplified "one-step" approach to the screen and diagnosis of gestational diabetes mellitus with a 75-gram, two-hour glucose tolerance test. The LabCorp test according to the ADA recommendations is Gestational Glucose Tolerance Screening and Diagnostics Test (Two-hour, ADA Recommendations) [101000]. A glucose tolerance screen glucose threshold >139 mg/dL after a 50-gram load identifies approximately 80% of women with gestational diabetes mellitus, while the sensitivity is further increased to approximately 90% by a threshold >129 mg/dL. Perform a diagnostic 100-gram oral glucose tolerance test (102004) on a separate day on women who exceed the chosen threshold on 50-gram screening.