Diabetes is the No. 6 leading causes of deaths in the United States, according to 2001 data from the United States National Center for Health Statistics.
Glucose Tolerance Test
Oral glucose tolerance test
The glucose tolerance test measures the body's ability to metabolize glucose.
How the test is performed
Glucose is the sugar that the body uses for energy. Patients with diabetes mellitus have high blood glucose levels. Glucose tolerance tests are one of the tools for making the diagnosis of diabetes.
The most common glucose tolerance test is the oral glucose tolerance test (OGTT). After an overnight fast, a patient drinks a solution containing a known amount of glucose. Blood is obtained before the patient drinks the glucose solution, and blood is drawn again every 30 to 60 minutes after the glucose is consumed for up to 3 hours.
Blood glucose levels above normal limits at the times measured can diagnose type 2 diabetes or gestational diabetes (high blood glucose during pregnancy). Insulin levels may also be measured. (Insulin is the hormone produced by the pancreas that moves glucose from the bloodstream into cells.)
The intravenous glucose tolerance test (IGTT) is not often used. In this test, patients are given a known amount of glucose by vein for 3 minutes, and blood insulin levels are measured before glucose and at 1 and 3 minutes. Insulin levels below a standard threshold may predict the development of type 1 diabetes in some patients.
How to prepare for the test
Fast for 12 hours and do not eat during the test. Consult your health care provider if you are using medication that can interfere with the test results. (See special considerations.)
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
The oral glucose tolerance test is used to screen pregnant women for gestational diabetes between 24 and 28 weeks of pregnancy. It may also be used to diagnose diabetes in research studies and in cases where the disease is suspected despite a normal fasting blood glucose.
For a 75-gram oral glucose tolerance test used to check for type 2 diabetes, normal (nondiabetic) blood values are:
For a 50-gram oral glucose tolerance test used to screen for gestational diabetes, normal blood values at 1 hour are less than 140 mg/dL.
For a 100-gram oral glucose tolerance test used to screen for gestational diabetes, normal blood values are:
Note: mg/dL = milligrams per deciliter
What abnormal results mean
Greater than normal levels of glucose may indicate
High glucose levels may be a manifestation of another clinical problem (for example, Cushing's syndrome).
What the risks are
Risks from venipuncture include:
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Several drugs may cause glucose intolerance, including the following:
Before having the test, let your health care provider know if you are taking any of these medications.
(From the National Institute of Health)