If you frequently exhibit symptoms of diabetes, such as excessive thirst, frequent urination, fatigue after eating or night sweats, your doctor may order an oral glucose tolerance test, or OGTT. The OGTT screens patients for diabetes mellitus and gestational diabetes by evaluating sugar metabolism after ingesting a dose of glucose. According to MedlinePlus, this three hour test can confirm the mildest case of diabetes.
Types of Tests
If your doctor suspects that you have diabetes, he may order one of four tests to confirm his diagnosis of diabetes. The three hour OGTT is commonly used among endocrinologists and obstetricians, but the intravenous glucose tolerance test is another option, though it's rarely used. According to MedlinePlus, your blood insulin levels will first be measured followed by an intravenous injection of a glucose solution. Your blood insulin levels are again measured at approximately one and three minutes after the injection; these timeframes may vary depending on your doctors preferences. An A1C blood test, which provides an average of your blood glucose levels for the past two to three months, and a one hour fasting glucose tolerance test are also options.
Test Preparation
According to the Mayo Clinic, you should eat and drink normally during the days preceding the test. You will be required to abstain from eating or drinking after midnight or eight to twelve hours before the test depending on your doctor's preferences. You will not be allowed to eat or drink anything during the test. Inform your doctor if you become ill before the test; tell him about any medications, prescription or over-the-counter, you may be taking as these can affect your test results. Because you will be fasting, consider choosing the earliest appointment available.
Test Administration
You will first submit a blood sample, which will be used to determine your fasting blood glucose level. You will then drink approximately 8 oz. of a sugary solution that contains 3.5 oz., or 99 g., of sugar. Your blood will then be drawn at one, two and three hours after ingesting the glucose solution. After the test, you may eat, drink and resume your normal daily activities. Some people feel nauseous and experience low energy after this test, so consider asking a friend or relative to drive you home.
Abnormal Results
The American Pregnancy Association has posted the four intervals of the three hour OGTT with corresponding abnormal blood glucose levels that are used to confirm diabetes. Fasting blood glucose levels should not exceed 95 mg/dL. At one hour after glucose consumption, blood glucose levels should not exceed 180 mg/dL. At two and three hours after consumption, blood glucose levels should not exceed 155 mg/dL and 140 mg/dL respectively.
Interpreting the Results
If two or more readings are abnormal during the OGTT, your doctor will diagnose you with diabetes. Together, you will create a treatment plan that best suits your needs and lifestyle that combines medicinal therapy with a healthy diet and daily physical activity or exercise. Depending on the severity of your disease, you may be able to adequately control your diabetes with oral medications. In more extreme cases, you may require daily injections or an insulin pump. Because prescription and over-the-counter medications or dietary supplements can elevate blood glucose levels or trigger adverse reactions, talk to your doctor before adding additional drugs to your daily regimen.
