Triiodothyronine (T3), Free

Triiodothyronine (T3), Free CPT: 84481

Synonyms

Free T3

T3, Free

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 – 2 days

Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.

Specimen Requirements

Specimen

Serum

Volume

0.8 mL

Minimum Volume

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

Container

Red-top tube or gel-barrier tube

Collection

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

Storage Instructions

Maintain specimen at room temperature.

Stability Requirements

Patient Information

Why Get Tested?

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 To Get Tested?

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

Sample Required?

A blood sample drawn from a vein in your arm.

Test Preparation Needed?

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.