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3 hour 100 gram Glucose Tolerance Test, Pregnancy

Item Value
Approval req'd? No
Available Stat? No
Test code OGTP
Test group Glucose
Performed by Parnassus & Mt. Zion Chemistry
In House Availability Test available at ACC 0730-1530 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 8-14 hour. fast.
Collection Instructions For outpatients, Please schedule in advance with the ACC outpatient lab, x32736, or Post St. lab, 415-885-7531. Outpatient testing at ACC available 0730-1530 weekdays, 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 Clinic will 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, do not proceed but refer the patient back to the Diabetes Clinic.

If the patient has not been screened using the 1-hour 50-gram test (or the Clinic does not indicate this), the fasting level to proceed with the 3-hour test must be ≤ 110 mg/dL.
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 < 95 mg/dL
1 hour < 180 mg/dL
2 hour < 155 mg/dL
3 hour < 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.
Last Updated 4/16/2014 10:19:47 AM
Entry Number 430
Lab Procedure Link Click here for Procedure
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