The oral glucose tolerance test can be useful in the diagnosis of diabetes mellitus, by following glucose levels after an oral glucose challenge.

Test Preparation:

(1) Starting 3 days prior to test, the patient receives a diet containing 150 g of carbohydrate per day.

(2) The patient must not be stressed by illness prior or during the test.

(3) All nonessential medications should be discontinued at least 3 days prior to testing; many medications can impair glucose tolerance.

(4) A 10-16 hour fast is recommended.

(5) Undue exercise before or during the test is to be avoided.


Dose of glucose for test:

(1) 1.75 gram per kilogram of ideal body weight, up to a maximum of 75 grams.

(2) Oral glucose solutions come in 10 US fluid ounces (296 mL) bottles containing 50, 75 or 100 grams of glucose (5, 7.5 and 10 g per fluid ounce).


A normal pediatric patient should have:

(1) a fasting glucose prior to the oral load < 100 mg/dL

(2) a glucose 2 hours after the oral dose < 140 mg/dL


An abnormal test may show:

(1) an elevated fasting glucose > 100 mg/dL

(2) a glucose > 200 mg/dL in a blood sample collected at 30, 60 or 90 minutes

(3) a glucose at 2 hours >= 140 mg/dL



• Both an elevated fasting glucose and a sustained elevated glucose during the oral tolerance test need to be present on at least 2 occasions to make the diagnosis of diabetes mellitus.

• The oral tolerance test is not needed if classic symptoms are present (polyuria, polydipsia, ketonuria, weight loss) and if a random glucose exceeds 200 mg/dL.


Previous guidelines for interpreting the oral glucose tolerance test:


Pediatric Patient


impaired glucose tolerance


< 140 mg/dL

< 140 mg/dL

30 minute (0.5 hour)

at least 1 of these must be >200 mg/dL


60 minute (1 hour)


90 minute (1.5 hour)


120 minute (2 hour)

> 200 mg/dL

140 - 200 mg/dL


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