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3 hour 100 gram Glucose Tolerance Test, Pregnancy

Item Value
Approval req'd? No
Available Stat? No
Test code OGTP, 3GT60, 3GT120, 3GT180
Test group Glucose
Performed by Parnassus, Mission Bay & Mt. Zion Chemistry
In House Availability Test available at ACC 0730-1400 weekdays. Test available at Mission Bay 0700-1400 weekdays. Test available at 2230 Post St. 0800-1400 weekdays.
Method Oxygen consumption (O2 electrode with glucose oxidase)
Patient Preparation The patient should be instructed by the care-giver to eat a normal diet containing at least 150 g of carbohydrate and carry out normal physical activity for at least 3 days prior to the morning of the test, which is administered after an 8-10 hour. fast.
Collection Instructions Outpatient testing at ACC available 0730-1400 weekdays, Mission Bay from 0700-1400 and at 2330 Post St. 0800-1400 weekdays.

The patient should be seated for the test and should not smoke.

Collect all samples in Gray top tubes<>/b>

Obtain a fasting sample and send to lab for stat testing. If the patient has been screened using the 1-hour 50-gram test (GLT1), the results of that test can help determine what the fasting level should be in order to proceed with the 3-hour 100 gram test. If the 1-hour 50-gram test result was ≥ 180 mg/dL the fasting glucose should be < 95 mg/dL to proceed with the 3-hour test. If the 1-hour 50-gram test result was 140-179 mg/dL, the fasting glucose should be < 110 mg/dL to proceed. If the fasting glucose is over these levels, call the Diabetes clinic and ask for instructions on whether to give the glucose or abort the test.

If the patient has not been screened using the 1-hour 50-gram test (or the Clinic does not indicate this), proceed with the test if the fasting glucose is < 92 mg/dL, If the fasting glucose levels is ≥92, the outpatient personnel must contact the Diabetes Clinic (3-2868) to inform them of the fasting glucose result and ask if the glucose loading should proceed.
Container type Gray top
Amount to Collect 1 mL blood Click here for Microdetermination info
Sample type Serum
Preferred volume 0.5 mL serum
Min. Volume 0.2 mL serum Click here for Microdetermination info
Units mg/dL
Normal range
Fasting 70-94 mg/dL
1 hour (post glucose) < 180 mg/dL
2 hour (post glucose) < 155 mg/dL
3 hour (post glucose) < 140 mg/dL

Synonyms Diabetes mellitus
Stability Room temperature 8 hours, refrigerated 2 days
Additional information This glucose tolerance test is part of a procedure to screen pregnant patients for gestational diabetes (GDM). Fasting glucose should be checked in all patients: 90% of patients whose 2 hour level is > 199 mg/dL have fasting hyperglycemia, obviating the need to schedule glucose tolerance testing.

Glucose tolerance screening for GDM may be performed as a one step approach or as a two step approach. This "3 hour 100 gram glucose tolerance test, pregnancy" is the second test in the two step screening approach for GDM. For the first test in the two step screening approach, see the "1 hour 50 gram glucose loading screen." A positive diagnosis in this second step test requires that two or more reference range thresholds be met or exceeded. For a discussion on the reference range for this test, see UpToDate section on "Screening for and diagnosis of diabetes mellitus during pregnancy."

For the one step approach to screening for GDM, see " 2 Hour, 75 gram Glucose Tolerance Test, Pregnant."

"Glucose tolerance beverages are available in 100 g bottles (10 g/fl. oz. at 10
oz.) at ACC, and 100 g and 50 g bottles (10 g/fl. oz., 5 g/fl. oz.both 10 oz.) at
Post St.

Source of reference range: UpToDate and the 4th International Workshop on Gestational Diabetes
CPT coding 82947
Last Updated 7/24/2017 5:09:05 PM
Entry Number 430
Lab Procedure Link Click here for Procedure
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