To confirm diabetes mellitus in selected patients

To aid in the diagnosis of hypoglycemia and malabsorption syndrome

Explain to the patient that the oral glucose tolerance test evaluates glucose metabolism.

Instruct the patient to maintain a high-carbohydrate diet for 3 days by consuming at least 150 g of carbohydrates per day for each of the 3 days, then fasting for 10 to 16 hours before the test.

Tell the patient not to smoke, drink coffee or alcohol, or exercise strenuously for 8 hours before or during the test.

Tell the patient that this test requires five blood samples and usually five urine samples.

Tell the patient that the procedure usually takes 3 hours but can last as long as 6 hours.

Alert the patient to the symptoms of hypoglycemia (weakness, restlessness, nervousness, hunger, and sweating) and tell her to report such symptoms immediately.

Notify the laboratory and physician of drugs the patient is taking that may affect test results; it may be necessary to restrict them.

Between 7 a.m. and 9 a.m., perform a venipuncture to obtain a fasting blood sample in a 7-ml clot-activator tube.

Collect a urine specimen at the same time if your facility includes this as part of the test.