Click here for more information about laboratory operations and procedures
Glucose Tolerance Test, Pregnancy
|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|
|Preferred volume||0.5 mL serum|
|Min. Volume||0.2 mL serum Click here for Microdetermination info|
|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|
|Lab Procedure Link||Click here for Procedure|
If you have additional questions regarding this test, please call: 415-353-1667