Glucose Tolerance Test


Posted on 10th May 2011 by admin in Uncategorized

A glucose tolerance test (GTT) is often requested to determine if a patient has carbohydrate metabolism problems.  Because glucose is the body’s major carbohydrate source of energy, a glucose tolerance test will show how well the body is able to metabolize glucose.  The GTT is also called the oral glucose test for major blood glucose disorders such as increased hyperglycemia and decreased hypoglycemia.  The GTT is able to evaluate the insulin levels that are regulated by the pancreas when a specific measurement of glucose is introduced into the body.  The glucose levels are recorded on blood specimens that are collected at specific intervals.  Insulin levels can also be measured if necessary.  Generally, a GTT is 1 hour for gestational diabetes and 3 hours for all other glucose evaluations.  Very rarely is it necessary for a test to go longer than 6 hours.  The results of the test are plotted on a graph  and create what is known as a GTT curve.

There are different doses of glucose and different timing intervals that can be done for various tests.  However, it is important that the method for blood collection is the same for all specimen collections.  For example, if the first specimen was collected by venipuncture than all subsequent collection should be acquired in the same manner.

The patient should be prepared for taking a GTT.  It is important that the patient eat balanced meals that contain approximately 150 grams of carbohydrates per meal for 3 days prior to the test.  The patient must also be advised to fast between 12 and 16 hours before the test.  The patient can drink water anytime during the fast or test but no other beverages or food can be consumed during this time.  The patient is also not permitted to smoke or chew gum during the fast or test because these actions stimulate the digestion and can cause inaccurate results.  To ensure compliance with these guidelines, a health-care provider should discuss verbally the requirements and also provide the patient with a written copy of the instructions to refer to, if necessary.

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