Oral Glucose Tolerance Test Procedure

Pre-Test Patient Preparation

The American Diabetes Association recommends that patients consume at least 150g of carbohydrate per day for a minimum of 3 days before the test, and maintain unlimited physical activity in the days leading up to the test, with no caloric intake for at least 8 hours before the test 5, 1, 2, 3, 4

The American Diabetes Association recommends administering 75g of anhydrous glucose dissolved in water for standard diabetes diagnosis, with venous plasma glucose measurements taken at fasting, 1-hour, and 2-hour time points 1, 2, 3, 4

The American Diabetes Association recommends diagnostic thresholds of fasting plasma glucose ≥126 mg/dL and 2-hour plasma glucose ≥200 mg/dL, with confirmation by repeat testing on a different day in the absence of unequivocal hyperglycemia 1, 2, 3, 4

The International Association of Diabetes and Pregnancy Study Groups recommends a one-step approach with a 75g glucose load and measurements at fasting, 1-hour, and 2-hour, with diagnostic thresholds of fasting ≥92 mg/dL, 1-hour ≥180 mg/dL, or 2-hour ≥153 mg/dL 6, 7
The National Institute of Diabetes and Digestive and Kidney Diseases recommends a two-step approach with an initial 50g glucose challenge test, followed by a 100g OGTT with measurements at fasting, 1-hour, 2-hour, and 3-hour if screening is positive, with diagnostic thresholds of at least two of the following: fasting ≥95 mg/dL, 1-hour ≥180 mg/dL, 2-hour ≥155 mg/dL, 3-hour ≥140 mg/dL 5, 8, 6, 7

The American Diabetes Association recommends that the test be performed in a certified laboratory using NGSP-certified methods standardized to the DCCT assay, and that high-risk pregnant women be tested at the first prenatal visit and retested at 24-28 weeks if negative 3, 4, 5, 6