A screening test for diabetes that involves testing an individual’s plasma glucose level after he drinks a solution containing 75 grams of glucose. Currently, a person is diagnosed with diabetes if his plasma glucose level is 200 mg/dl or higher two hours after ingesting the glucose. Those with a plasma glucose level less than 200 mg/dl but greater than or equal to 140 mg/dl are diagnosed with a condition called impaired glucose tolerance, or prediabetes. People with this condition have trouble metabolizing glucose, but the problem is not considered severe enough to classify them as having diabetes. Individuals with impaired glucose tolerance are at a slightly elevated risk for developing high blood pressure, blood lipid disorders, and Type 2 diabetes.
According to the American Diabetes Association, the OGTT is not necessary to diagnose diabetes and should rarely be used. The screening test of choice for diagnosing diabetes is the fasting plasma glucose test, which measures a person’s plasma glucose level after he has fasted (not eaten) for at least eight hours. This test is favored because it is simpler, more accurate, less expensive, and less variable than the OGTT.