The Lab Policy and Procedure for a Glucose Tolerance Test

An Overview of Glucose

Glucose levels are regulated by the pancreas, and this is the chemical that the hormones insulin and glucagon will act on. In the condition called diabetes, the body has a high blood sugar level. There are various ways to test for diabetes, and the oral glucose tolerance test is one of the methods to determine if the person has diabetes.

Why Is The Test Ordered & How is The Test Performed

The person is instructed to fast until after the test is completed. A sample of blood will be taken to determine the fasting blood glucose level. The person will be given a container of liquid with a known concentration of glucose inside of it. After drinking this liquid, the person’s blood will be drawn at least a half an hour to an hour after consumption. There is also another intravenous glucose tolerance test but it has become antiquated as it requires the person have blood drawn, be injected with a solution of glucose, and then have blood drawn again after the test to compare the glucose levels.

The glucose tolerance test policy and procedure states that this test is used to measure how the body responds to glucose loading, if a large dose of glucose is given. According to the glucose tolerance test lab policy and procedure, this test is used to determine if the person has type 2 diabetes mellitus.

Another reason the glucose tolerance test may be administered is to evaluate the effectiveness of current diabetic treatment.

This test is also used in pregnant women to determine if they have gestational diabetes. This is diabetes resulting from the stress of pregnancy on the woman’s body. However, instead of giving a loading dose of 75 grams of glucose, a pregnant woman is only given 50 grams of glucose as a loading dose.

Blood Test Results

A positive test result, as per glucose tolerance test lab guidelines, can be received if there is a significant measurement in the person’s blood glucose level before and after the glucose loading. In regards to the normal results that is expected with the oral glucose test, before the glucose is given, the fasting blood sugar level should between 60 to 100 mg/dl. It is expected that the normal blood gluose level after the glucose is given is should be less than 200 mg/dl. If the blood results show that blood glucose level is between 140 to 200 mg/dl after the loading dose is given, the person is though to have impaired glucose tolerance and may develop diabetes in the future.


Print Source: Cotran R, Kumar V, and Robbins, SL. 1999. Robbins Pathologic Basis of Disease, 6th Ed. W.B. Saunders Company, Philadelphia.

Web Source: U.S. National Library of Medicine. "Diabetes.” 2010. Available: