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Test Code GT3HR Glucose Tolerance Test, Gestational; 100 Gm Load LAB164

Test Method

Timed Endpoint; Beckman DXC600

Specimen Requirement

0.5 mL serum or plasma is required.

Additional Specimen Collection Information

Collect blood in a lithium heparin, green-top or red-top
tube fasting and at specified time intervals after the patient has
consumed 100 gm of Trutol. PST and SST (gel tubes) are acceptable.
Samples with ≥ 3+ lipemia must be cleared prior to analysis.
The serum or plasma must be physically separated from the cells
within 2 hours of collection.

  • The test is administered in the morning following a fast of
    between 8-10 hours. The fasting specimen must be tested and within
    normal range before Trutol is administered.
  • The patient should have had at least 3 days of unrestricted
    diet and normal physical activity. Instruct the patient to remain
    seated or reclined throughout the procedure.
  • The patient may have water to drink but nothing else. Coffee
    and smoking materials are prohibited.
  • The NIH (National Institute of Health) recommends 3 hours
    in pregnant subjects, with an additional specimen collected at the
    first and third hour.
  • A physician can request a longer OGTT (Oral Glucose
    Tolerance Test) with different dosages and specimen collection
    intervals. Consult a pathologist when this occurs.

Reference Values

“Gestational diabetes” if 2 or more patient values fall within
the following parameters :

  • Fasting: ≥ 95 mg/dL
  • 1 hour: ≥ 180 mg/dL
  • 2 hour: ≥ 155 mg/dL
  • 3 hour: ≥ 140 mg/dL


Testing is performed Monday through Friday.

Same day turn around time.

Useful For

Diagnosis of Gestational Diabetes Melitis

LOINC Code Information

50608-9 Glucose Tolerance 3 Hours Gestational Panel-Serum Or

CPT Code Information

82951 Chemistry: Glucose Testing Glucose; tolerance test (GTT),
3 specimens (includes glucose)

82952 Chemisty: Glucose Testing Glucose; tolerance test (GTT),
each additional beyond 3 specimens (List separately in addition to
code for primary procedure)