ABBR: OGTT

A screening test for diabetes mellitus (DM), in which plasma glucose levels are measured after the patient consumes an oral glucose load. In screening patients for type 2 DM, measuring fasting plasma glucose levels or checking a hemoglobin A1c level is generally preferable to an OGTT because the former tests are simpler, cheaper, and better tolerated by patients. An OGTT reveals type 2 DM when plasma glucose levels exceed 200 mg/dL 2 hr after drinking a 75-g glucose load. Plasma glucose levels between 140 mg/dL and 199 mg/dL suggest impaired glucose tolerance.

Gestational Diabetes Mellitus: In pregnancy, a modified OGTT is used to screen women with risk factors for gestational diabetes (GDM), including obesity, family history of type 2 DM, age greater than 25 years, and a history of unexplained stillbirths. At 24 to 28 weeks' gestation, a 50-g glucose load is given; 1-hr plasma glucose levels greater than 140 mg/dL constitute a positive screening result. Any patient having a positive test result should then undergo a 2-hr, 100-g OGTT to determine whether GDM is present. Alternatively, an expectant mother can consume a single 75-g oral glucose load. A blood glucose above 140 mg/dL 2 hr after the test is diagnostic of diabetes mellitus in pregnancy.