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Oral glucose tolerance test

Oral glucose tolerance test measures how well your body’s cells are able to absorb glucose, or sugar after you ingest a given amount of sugar. This test was the gold standard for making the diagnosis of type 1 and type 2 diabetes and prediabetes. The test is used to determine whether the body has difficulty metabolizing intake of sugar/carbohydrate. It is still commonly used during pregnancy for diagnosing gestational diabetes.

Oral glucose tolerance test – Individual should be on a normal diet for 3 days, and fasting overnight (10-16 hours). Before the test, you will be asked not to eat, or drink certain fluids, for up to 8 to 12 hours before the test.

(1) Collect fasting venous blood for plasma and corresponding urine.

(2) Give 75 gm (WHO declared) or (1 gm/kg of body wt.) glucose in 250-300 ml of water by mouth.

(3) Collect venous blood and urine sample –

  • At the end of 2 hours or,
  • At half hourly interval for 2-2.5 hours.

(4) Estimation of blood glucose, and Estimation of a urine sample.


In a normal person: Alter ingesting glucose, the blood glucose level rises from about 90mg/100ml to 120 or 140mg/100ml and falls back to below normal in about 2 hours.

In a diabetic patient: After ingesting glucose, the blood glucose level rises more than 200mg/dl and the glucose level falls back to the control value after 4-6 hours; furthermore, it fails to fall below the control level.


  1. One of the important diagnostic tool of DM.
  2. It also helps in diagnosing hypocalcemic malabsorption syndrome or crushing syndrome.