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1- hour 50 gram Glucose Loading Screen

Item Value
Approval req'd? No
Available Stat? No
Test code GLT1
Test group Glucose
Performed by Parnassus, Mission Bay & 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)
Collection Instructions Schedule in advance with ACC outpatient phlebotomy, x32736 or Post St. lab 415-885-7531 (Mt. Zion). This screening test may be given at any time of day, without regard to prior meals.
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 1 hour post-50 g po glucose, without regard to whether patient had been fasting: 70 -139 mg/dL
Synonyms Diabetes mellitus; GCT; Glucose challenge test
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 "1 hour 50 gram glucose loading screen" is the first test used as part of a two step screening approach. Patients who screen abnormal in this test proceed to the second step, a "3 hour 100 gram Glucose Tolerance Test, Pregnancy." The optimal reference range for this first step of the two step screening approach is controversial. For a discussion on the reference range for this test, see UpToDate section on "Screening for and diagnosis of diabetes mellitus during pregnancy."

For a one step approach to screening for GDM, see " 2 Hour, 75 gram Glucose Tolerance Test, Pregnant."
LOINC code 1558-6
Last Updated 1/28/2015 2:36:06 PM
Entry Number 429
Lab Procedure Link Click here for Procedure
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