Triiodothyronine (T3), Free

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Category:

Turnaround Time: 1 - 2 days
CPT Code:

84481

Test Type: 0.8 mL Serum
Stability Time:

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3
Reference Range:

See table.1

Age

Range (pg/mL)

0 to 3 d

2.0−7.9

4 to 30 d

2.0−5.2

31 d to 12 m

1.6−6.4

13 m to 5 y

2.0−6.0

6 to 10 y

2.7−5.2

11 to 19 y

2.3−5.0

>19 y

2.0−4.4

Overview:

Evaluate thyroid function and assess abnormal binding protein disorders.

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

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. PubMed 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. PubMed 402243

Collection Details:

Collection 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.

Red-top tube or gel-barrier tube.

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

Room temperature.