To prepare for a glucose tolerance test, a patient refrains from eating or drinking for eight hours prior to the test, according to Mayo Clinic. In the days leading up to the test, the patient should eat and drink as she normally does. If the patient is ill or taking any medications, she should inform her doctor of these facts, to avoid inaccurate test results.
When using the glucose tolerance test to check for type 2 diabetes, the patient arrives at her doctor's office after undergoing the eight-hour fast, and has a blood sample drawn from a vein in her arm, states Mayo Clinic. The patient then drinks an eight-ounce glucose solution that is thick and sugary, waits for two hours, and then has her blood drawn again. Pregnant women sometimes undergo a similar test, but with a one-hour wait period, between the 24th and 28th weeks of pregnancy. This is for women with high-risk factors such as metabolic syndrome, polycystic ovary syndrome, family history of diabetes, obesity, or gestational diabetes during an earlier pregnancy.
A three-hour glucose tolerance test is indicated for a patient who has risk factors for gestational diabetes or whose one-hour test resulted in a suspicious value, according to the Mayo Clinic. The three-hour test is the same as the one- and two-hour tests, except that the patient's blood is drawn three times, once per hour, for three hours after she drinks the glucose solution.