triiodothyronine [T3] (free) in serum
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Indications
- suspected T3 thyrotoxicosis
* rarely necessary
Reference interval
Clinical significance
- free T3 is the active form of plasma T3
- 0.2-0.5% of total plasma T3 exists unbound as free T3,
- compare with free T4 0.02-0.04%
- normally, T3 total in serum represents ~5% of thyroid hormone in serum
- T3 is more active than T4, estimates range from 3-100 fold more active
- serum free T3 is inversely related risk of mortality[6]
- serum free T4 is positively related risk of mortality[6]
* assays are highly variable[5]
Methods
- equilibirum dialysis immunoassay
Specimen
- serum, refrigerate immediately, stable for 7 days at room temp, but storage at 4 C preferred
More general terms
Additional terms
References
- ↑ Jump up to: 1.0 1.1 Clinical Guide to Laboratory Tests, 3rd edition, NW Tietz ed, WB Saunders, Philadelphia, 1995
- ↑ Jump up to: 2.0 2.1 Medical Knowledge Self Assessment Program (MKSAP) 15, American College of Physicians, Philadelphia 2009
- ↑ Triiodothyronine, Free (Free T3) Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0070133.jsp
- ↑ Free T3 by Equil Dialysis-TMS Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0093243.jsp
- ↑ Jump up to: 5.0 5.1 Krouss M et al. Free the T3: Implementation of best practice advisory to reduce unnecessary orders. Am J Med 2022 Dec; 135:1437. https://www.amjmed.com/article/S0002-9343(22)00571-X/fulltext
- ↑ Jump up to: 6.0 6.1 6.2 Lawton RI et al Longevity, demographic characteristics, and socio-economic status are linked to triiodothyronine levels in the general population. Proc Natl Acad Sci USA. 2014. Jan 9;121(2):e2308652121 PMID: https://www.ncbi.nlm.nih.gov/pubmed/38175866 PMCID: PMC10786306 Free PMC article https://www.pnas.org/doi/10.1073/pnas.2308652121