Triiodothyronine (T3), Free

CPT: 84481
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  • 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

1 - 2 days

Related Documents

For more information, please view the literature below.

Thyroid Testing: Assessing Thyroid Disease in Your Patients

Specimen Requirements


Serum (preferred) or plasma


1 mL

Minimum Volume

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


Red-top tube, gel-barrier tube, or green-top (lithium heparin) tube. Do not use oxalate, EDTA, or citrate plasma.


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

Storage Instructions

Room temperature

Stability Requirements



Room temperature

14 days


14 days


14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Citrate plasma specimen; improper labeling

Test Details


Evaluate thyroid function and assess abnormal binding protein disorders


Circulating antibodies to thyroid hormones have also been reported to interfere with free hormone immunoassays.


Electrochemiluminescence immunoassay (ECLIA)

Reference Interval

See table.1


Range (pg/mL)

0 to 3 d


4 to 30 d


31 d to 12 m


13 m to 5 y


6 to 10 y


11 to 19 y


>19 y


Additional Information

Triiodothyronine (T3) normally represents only approximately 5% of the thyroid hormone and like thyroxine is almost entirely bound to the carrier proteins, with only 0.25% of the total being in the free state. Measurement of free triiodothyronine is of value in confirming the diagnosis of hyperthyroidism, when an elevated free or total thyroxine level is found. Abnormal total and free triiodothyronine concentrations may appear in T3 toxicosis, in the presence of normal thyroxine levels. Free T3 levels are unaffected by carrier protein variation.


1. Reference Intervals for Children and Adults. Elecsys Thyroid Test. Roche Diagnostics; May 2005.8595709


Albertini A, Ekins RP, eds. Free Hormones in Blood. Amsterdam, Holland: Elsevier Biomedical Press;1982.
Parslow ME, Oddie TH, Fisher DA, et al. Evaluation of serum tri-iodothyronine and adjusted tri-iodothyronine (free tri-iodothyronine index) in pregnancy. Clin Chem. 1977 Mar; 23(3):490-492. 402243


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
010389 Triiodothyronine (T3), Free 3051-0 010389 Triiodothyronine (T3), Free pg/mL 3051-0

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