Triiodothyronine (T3), Free

CPT: 84481
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Test Details

Synonyms

  • Free T3
  • T3, Free

Use

Evaluate thyroid function and assess abnormal binding protein disorders

Limitations

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

Methodology

Electrochemiluminescence immunoassay (ECLIA)

Reference Interval

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

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.

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

Room temperature

Stability Requirements

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

Causes for Rejection

Citrate plasma specimen; improper labeling

Clinical Information

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.

Footnotes

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

References

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

LOINC® Map

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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