Description of the test
The glucose tolerance test measures the body's ability to use glucose. Glucose is a type of sugar found in the blood. Glucose levels, also called blood sugar levels, are regulated by the hormone insulin. When insulin works properly, blood sugar levels in the blood remain controlled. If insulin does not work properly or the body does not produce enough insulin, you may have diabetes. The glucose tolerance test helps doctors determine if you have diabetes. It can also identify hypoglycemia (low blood sugar).
Testing can be done in a doctor's office, clinic, or hospital.
Blood that requires testing in a laboratory
How often should this test be performed?
The test is routinely used during pregnancy to determine whether a woman has developed gestational diabetes (a temporary form of diabetes caused by pregnancy). It can also be used on a regular basis to screen people who are at risk of diabetes. In special circumstances, it is used to check for hypoglycemia, or low blood sugar.
Why is this test performed?
This test helps the doctor determine if you have diabetes. It also helps determine if you have another condition that affects blood glucose levels (e.g., Cushing's syndrome, celiac disease, cystic fibrosis, acromegaly, pheochromocytoma, hemochromatosis, Addison's disease, hypothyroidism, hypoglycemia, or cirrhosis).
Are there any risks and precautions I should know about?
Although the glucose tolerance test is considered safe, it does have some risk of side effects or complications. Though rare, the side effects or complications may include:
- infection, if the area is not properly sterilized before the sample is taken
- excess bleeding from the area that was punctured
- bruising where the needle was inserted
You will be monitored throughout the test to make sure that your blood glucose level does not drop too low. You may experience weakness, sweating, anxiety, hunger, or other symptoms if this happens. Be sure to tell the person performing the test if you experience any of these symptoms.
People with bleeding disorders or anyone taking medication that reduces the ability of the blood to clot (e.g., warfarin, aspirin, or other anticoagulants) should tell the technician before the samples of blood are taken. These conditions and medications may require special attention at the time of testing.