09 May, 2010

Glucose Tolerance Test.

What is the glucose tolerance test?

The oral glucose tolerance test (OGTT) is the gold standard for making the diagnosis of type 2 diabetes. With an oral glucose tolerance test, the person fasts overnight (at least 8 but not more than 16 hours). Then first, the fasting plasma glucose is tested. After this test, the person receives 75 grams of glucose Blood samples are taken in 1st hour and 2nd hour.

Prerequisites for GTT

The person should be normally active and should not be taking medicines that could affect the blood glucose. For three days before the test, the person should have eaten a diet high in carbohydrates (150- 200 grams per day). The morning of the test, the person should not smoke or drink coffee/tea.

The classic oral glucose tolerance test measures blood glucose levels three times over a period of 2 hours. In a person without diabetes, the glucose levels rise and then fall quickly. In someone with diabetes, glucose levels rise higher than normal and fail to come back down as fast.

Glucose tolerance test- inference

Normal response: Fasting value < 100 mg/dl and 2nd hour value < 200 mg/dl

Impaired glucose tolerance: fasting glucose is less than 126 mg/dl and the 2-hour glucose level is between 140 and 199 mg/dl.

Diabetes: Fasting glucose is noted as greater than 126 mg/dl and 2nd hour sample more than 200mg/dl


  1. What you have mentioned is ADA criteria.we follow WHO.it is >= and <=.

  2. Dear Dr.Deepa,
    thanks for ur comments. i have mentioned only ADA guidelines as its easy for everyone to understand. the only diff b/w ADA & WHO is the fasting blood sugar levels. but still let me fulfill ur wish.. here comes ur WHO criteria.

    Fasting plasma glucose ≥7.0mmol/l (126mg/dl)
    2–h plasma glucose ≥11.1mmol/l (200mg/dl)

    Impaired Glucose Tolerance (IGT)
    Fasting plasma glucose <7.0mmol/l (126mg/dl)
    2–h plasma glucose ≥7.8 and <11.1mmol/l
    (140mg/dl and 200mg/dl)

    Impaired Fasting Glucose (IFG)
    Fasting plasma glucose 6.1 to 6.9mmol/l
    (110mg/dl to 125mg/dl)
    2–h plasma glucose <7.8mmol/l (140mg/dl)


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