Glucose Tolerance Test (GTT) Blood Test, 3-Hour, 4 Specimens
A GTT Blood Test or 3-Hour Glucose test assesses 4 Specimens is ordered for the screening and diagnosis of diabetes mellitus.
The 3-hour Glucose test requires individuals to fast for 10 – 12 hours before giving blood for the test. Individuals are allowed to drink water and to take medications during the fast.
Why It Is Used
The 3-hour glucose tolerance test (GTT) is primarily used to determine the presence of diabetes. The test is also used to detect health complications that are a result of diabetes.
How It Works
This test involves four blood draws, is conducted over the course of three hours, and, in general, requires the person taking the test to remain in the lab for the entire duration of the test. So, one of the most important things one can do to prepare for this blood test is to pick a great book to use for entertainment while sitting at the lab. Also, the test needs to be scheduled early enough that the lab will be open for at least three hours after the test begins.
Before one arrives at the lab he or she is required to have fasted for 10-12 hours. The first blood draw will be taken upon arrival to the lab. The individual will then be given a drink that contains 75 grams of glucose. The next three blood draws will be taken at 1 hour, 2 hours, and 3 hours after the glucose drink is consumed. This test is used to assess how an individual processes glucose. Glucose is a blood sugar that enters the blood after food is introduced to the body. The pancreas then releases insulin to move the glucose out of the blood so that it can be stored for energy in tissue and fat cells. In a person with diabetes the insulin process does not work effectively, and so glucose levels in the blood remain high longer than they should.
Test results are interpreted by looking at the levels of glucose found in the blood. Glucose is measured in milligrams per deciliter (mg/dL). Normal results vary based of what test is being used. The following results are representative numbers based on the glucose tolerance test, 3hr (4 Blood Specimens).
- After fasting: blood glucose levels above 95 mg/dL after fasting fall within the abnormally high range glucose levels.
- Glucose drink 1 hr: blood glucose levels above 180 mg/dL one hour after drinking 75 grams of glucose fall within the abnormally high range glucose levels.
- Glucose drink 2 hr: blood glucose levels above 155 mg/dL two hours after drinking 75 grams of glucose fall within the abnormally high range glucose levels.
- Glucose drink 3 hr: blood glucose levels above 140 mg/dL three hours after drinking 75 grams of glucose fall within the abnormally high range glucose levels.
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