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Test Code GT2HR Glucose Tolerance Test (OGTT) LAB169

Test Method

Timed Endpoint; Beckman DXC600


Testing is performed Monday through Friday.

Same day turn around time.

Useful For

Diagnosis of Diabetes Melitis

Specimen Requirement

0.5 mL serum or plasma is required.

CPT Code Information

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

Reference Values

Normal Results:

Adults (nonpregnant)

    Fasting: < 100 mg/dL
    2 hour: < 140 mg/dL

OGTT diagnostic criteria: (American Diabetes Association; 1999)

     Adults (nonpregnant) with diabetes
        Fasting: ≥ 126
mg/dL on more than one occasion
        2 hour: ≥ 200
    Adults (nonpregnant) with impaired glucose
        Fasting: ≥ 100 and
< 126 mg/dL
        2 hour: ≥ 140 and
< 200 mg/dL
    Pregnant subjects with gestational diabetes must
meet 2 or more of the following criteria:
        Fasting: ≥ 95
        1 hour: ≥ 180
        2 hour: ≥ 155
        3 hour: ≥ 140

Critical Value: < 50 mg/dL and > 450 mg/dL


LOINC Code Information

72171-2 Glucose Tolerance 2 Hours Panel-Serum Or Plasma

Additional Specimen Collection Information

Collect blood in lithium heparin green-top or red-top tube from
a fasting patient. PST and SST (gel tubes) are acceptable. The
fasting specimen is assayed prior to the patient consuming the
glucose drink. If the fasting result is acceptable the patient is
given the appropriate quantity of glucose drink.

500 mcL of serum or lithium heparin plasma collected at
specified time intervals after the patient has consumed 100 gm of
glucose drink. 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.

  • Fasting specimen must be tested and less than 126 mg/dl before
    the glucose drink is given.
  • If the fasting glucose is ≥ 126 mg/dL contact the
    ordering physician before continuing the tolerance test.
  • If the physician is not available contact a pathologist before
  • 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.
  • Children under 16 years will be given a glucose load based upon
    their actual body weight. Include information regarding child’s
    weight when requesting the test.
  • The test is administered in the morning following a fast of
    between 8-10 hours.
  • The NIH (National Institute of Health) recommends a 2 hour
    procedure with blood collected at fasting and 2 hours; (3 hour
    procedure in pregnant subjects, with an additional specimen
    collected at the first and third hour. See Glucose Tolerance
  • A physician can request a longer OGTT (Oral Glucose Tolerance
    Test) with different dosages and specimen collection intervals.
    Consult a pathologist when this is ordered.