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Test Code 127 Glucose Tolerance Test (OGTT)

Additional Codes


PowerChart: Glucose Tolerance 2 Hours


Specimen Requirement

0.5 mL serum or plasma is required.

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 proceeding.
  • 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 Gestational.)
  • 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.

Useful For

Diagnosis of Diabetes Melitis


Testing is performed Monday through Friday.

Same day turn around time.

CPT Code Information

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

LOINC Code Information

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

Test Method

MercyOne DBQ:

Timed Endpoint; Beckman DXC880i

Mercy DV and MQMA:

Catalytic Oxidation Electrode; iSTAT

MA East and West:

Enzymatic Colorimetric Method; Roche Cobas 6000

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 mellitus:
        Fasting: ≥ 126 mg/dL on more than one occasion
        2 hour: ≥ 200 mg/dL
    Adults (nonpregnant) with impaired glucose tolerance:
        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 mg/dL
        1 hour: ≥ 180 mg/dL
        2 hour: ≥ 155 mg/dL
        3 hour: ≥ 140 mg/dL

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