The oral glucose tolerance test can be useful in the diagnosis of diabetes mellitus, by following glucose levels after an oral glucose challenge.
(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:
impaired glucose tolerance
< 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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Specialty: Endocrinology, Clinical Laboratory