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Lab Manual for Moffitt-Long and Mount Zion

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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 All patients should be screened with a fasting glucose: 90% of patients whose 2 hour level is > 199 mg/dL have fasting hyperglycemia, obviating the need for tolerance testing.

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.

Note: A positive diagnosis requires that two or more thresholds be met or exceeded. Reference values for the 100 gram 3 hour GTT are taken from American College of Obstetricians and Gynecologists. Committee opinion no. 504: screening and diagnosis of gestational diabetes mellitus.
Obstet Gynecol 2011;118:751–3.

Additionally, there is controversy regarding the approaches used to diagnose gestational diabetes Blackwell SC. Counterpoint: enough evidence to treat? The American College of Obstetricians and Gynecologists guidelines. Clin Chem. 2012 Jul;58(7):1098-100.
Last Updated 12/19/2012 2:01:03 PM
Entry Number 430
Lab Procedure Link Click here for Procedure

If you have additional questions regarding this test, please call: 415-353-1667

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