Oral glucose tolerance test (OGTT) is a medical test in which a standard dose of glucose is administered orally & then blood sample is taken at set times to see how quickly the glucose is utilized by the body & cleared off from blood. OGTT is used as a confirmatory test to diagnose diabetes & can indicate presence of pre-diabetes (insulin resistance).
OGTT is advised to individuals at high risk of developing diabetes or those with impaired sugar levels.
Following are the important considerations:
1. The test is done after at least 3 days of unrestricted diet & normal physical activity.
2. The test is never done during any illness because blood sugar levels may fluctuate due to the underlying infection, medicines or illness.
3. It is carried out in resting conditions. Vigorous activities are not allowed during the test.
4. Smoking is not allowed on the morning as well as during the test.
5. Usually the OGTT is performed in the morning.
Steps involved in OGTT:
1. The person is instructed to fast for 10-16 hours during which drinking plain water is permitted.
2. Fasting blood sample is collected.
3. 75 grams glucose is dissolved in 250 – 300 ml of water & it should be drunk by the person over the course of about 5 minutes.
4. Another blood sample is collected 2 hours after the glucose load.
If one is diagnosed to have pre-diabetes, it is important to have OGTT repeated at 12 months initially; then as indicated by the results.
Following table gives interpretation of OGTT-
(Blood sugar values in mg/dL)