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Free T3, Adult

Item Value
Test Update Information Effective March 19, 2013, the Free T3 assay changed from the Abbott Axsym to the Abbott Architect i2000 analyzer. NOTE new reference range and change in units of measurement from pg/dL to pmol/L. Conversion formula: (Concentration in pg/dL) x (.01536)= concentration in pmol/L
Clinical Questions Does my patient have autoimmune thyroiditis?
Approval req'd? No
Available Stat? No
Test code FT3
Test group Thyroid tests
Performed by China Basin Chemistry
In House Availability Monday - Saturday (day shift)
Method Two step chemiluminescent Microparticle Immunoassay (Abbott Architect i2000)
Container type Gold top or Light Green top
Amount to Collect 2 mL blood
Sample type Serum or plasma
Preferred volume 1 mL serum or plasma
Min. Volume 0.5 mL serum or plasma
Processing notes Refrigerate
Units pmol/L
Normal range
Adults (18 years and older) 2.6-5.7 pmol/L

For children, order test Free T3, Pediatric (code PFT3)

Adult reference ranges adopted from manufacturer reference range studies (95% CI) and verified in-house using blood donor (N=124) (excluding autologous donors) on no medications and negative for anti-Tg and TPO antibodies.
Synonyms Triiodothyronine
Turn around times 0 to 2 days
Additional information T3 circulates in the blood as an equilibrium mixture of free and protein bound hormone. T3 is bound to thyroxine binding globulin (TBG), prealbumin, and albumin. The binding of these proteins is such that only 0.2-0.4% of the total T3 is present in solution as unbound or free T3. This free fraction represents the physiologically active thyroid hormone. Occasionally, FT3 alone is elevated (T3 thyrotoxicosis) in about 5% of the hyperthyroid population. FT3 may also be important in monitoring patients on antithyroid therapy where treatment is focused on reducing the T3 production and the T4 conversion to T3. Serum FT3 may also be useful in assessing the severity of the thyrotoxic state.
CPT coding 84481
LOINC code 3051-0
Last Updated 6/20/2016 1:29:07 PM
Entry Number 1038
Lab Procedure Link Click here for Procedure
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