Gestational Glucose Tolerance Screening and Diagnostic Test (Two-hour, ADA Recommendations)
Also known as: Glucose Tolerance Test, Gestational (Fasting, One-hour, and Two-hour)
Use
Screening and diagnosis of gestational diabetes
Special Instructions
For patient preparation, patients should be active and consume a regular diet with at least 150 grams of carbohydrates daily for three days prior to the test. It's important that patients fast for at least eight hours and not more than 14 hours before the test, during which time they can only drink water. Whenever possible, discontinue all nonessential medications that affect glucose metabolism at least three days before testing.
Limitations
The test uses a 75-gram glucose load for the oral glucose tolerance test; varying from the recommended pre-test preparation can affect test results. It is significant to ensure correct labeling of samples with collection intervals; failed identification of samples by time interval can result in sample rejection. Individuals under stress conditions such as recent surgery, infection, or undergoing corticosteroid therapy should not have the Glucose Tolerance Test as these conditions can also affect the results. The methodology utilizes an enzymatic process which may have technical limitations based on specific conditions or interferences.
Methodology
Automated Analyzer (Clinical Chemistry)
Biomarkers
LOINC Codes
- 93794-6
- 1558-6
- 1507-3
- 1518-0
Result Turnaround Time
1 day
Related Documents
For more information, please review the documents below
Specimen
Serum
Volume
1 mL serum each tube
Minimum Volume
0.5 mL serum each tube
Container
Gel-barrier tubes (3)
Collection Instructions
Draw a fasting blood sample before administering glucose. Administer a 75-gram glucose and draw blood after one hour and two hours. The patient should remain seated throughout the test. Submit 1 mL serum for fasting, one-hour, and two-hour specimens. Separate serum from cells within 45 minutes of venipuncture. Gel-barrier tubes should be used.
Patient Preparation
Patient should be active and eat a regular diet that includes at least 150 grams of carbohydrate daily for three days prior to the test.
Storage Instructions
Maintain specimen at room temperature.
Causes for Rejection
Frozen gray-top tube (frozen plasma from gray-top is acceptable); stressed patient (surgery, infection, corticosteroids) should not have GTT; specimens not labeled with collection time intervals (i.e., fasting, one-hour, and two-hour)
Stability Requirements
| Temperature | Period |
|---|---|
| Room Temperature | 14 days |
| Refrigerated | 14 days |
| Frozen | 14 days |