The glucose tolerance test is a blood test that is used to check blood glucose levels in order to screen for either gestational or type 2 diabetes. The test involves a period of fasting, then ingesting a quantity of glucose. The blood glucose level is tested one or more times after the glucose is ingested. An individual’s results are compared to the expected numbers. If the glucose tolerance test results show a blood glucose level out of line with acceptable levels, it indicates the possibility of diabetes or other health problems.
To prepare for blood glucose testing, the patient should maintain a normal diet and daily schedule for a week or so before the test. He or she must then fast for at least eight hours immediately prior to the test. Tthe patient must also not have anything to drink during those eight hours.
How the test is administered depends on whether a person is being tested for type 2 diabetes or gestational diabetes. Testing for type 2 diabetes involves drawing blood once, two hours after the patient drinks a sugary drink containing a measured amount of glucose. When testing for gestational diabetes, which is the type of diabetes that can occur during pregnancy, blood is drawn at least once, and may be drawn several times over a period of hours after the glucose solution has been ingested.
In order to interpret the glucose tolerance test results, blood test results are compared to levels that are considered within normal rangel. Normal levels for a non-pregnant person are 140 mg/dL (milligrams per deciliter), and for a woman who is pregnant they run about 95 mg/dL. Two hours after drinking the solution, glucose tolerance test results should be under 200 mg/dL in the type 2 diabetes test and 155 mg/dL when screening for gestational diabetes. These values may differ somewhat with different doctors or laboratories, but are generally considered good average results.
When the glucose tolerance test results show numbers higher than the average, it may be an indicator of diabetes, requiring further diagnostic testing. Glucose tolerance test results may also be affected by illness, stress, or medication. These factors must also be taken into account when interpreting the test results, since they may lead to abnormal levels even though there is no medical problem present. Results above the normal levels may also indicate other illnesses besides diabetes, also requiring further diagnostic testing and a thorough review of the patient's history.