Triiodothyronine (T3) CPT: 84480


T3, Total

Special Instructions

This test may exhibit interference when sample is collected from a person who is consuming a supplement with a high dose of biotin (also termed as vitamin B7 or B8, vitamin H, or coenzyme R). It is recommended to ask all patients who may be indicated for this test about biotin supplementation. Patients should be cautioned to stop biotin consumption at least 72 hours prior to the collection of a sample.

Expected Turnaround Time

Within 1 day

Specimen Requirements




0.8 mL

Minimum Volume

0.3 mL (Note: This volume does not allow for repeat testing.)


Red-top tube or gel-barrier tube.


If a red-top tube is used, transfer separated serum to a plastic transport tube.

Storage Instructions

Room temperature.

Stability Requirements

Temperature Period
Room Temperature Not recommended
Refrigerated 7 days
Frozen 4 weeks
Freeze/thaw/ cycles Stable x 3

Patient Information

To help evaluate thyroid gland function; to diagnose thyroid disease, including hyperthyroidism, and determine the cause; to monitor effectiveness of treatment of a thyroid disorder.

When you have an abnormal thyroid stimulating hormone (TSH), particularly with a normal free thyroxine (T4) result, and/or signs and symptoms of hyperthyroidism.

A blood sample drawn from a vein in your arm.

None needed; however, certain medications, multivitamins and supplements can interfere with the free T3 and total T3 tests, so tell your healthcare practitioner about any prescribed or over-the-counter drugs and/or supplements that you are taking. Acute illness may affect thyroid testing test results. It is generally recommended that thyroid testing be avoided in hospitalized patients or deferred until after a person has recovered from an acute illness.