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Test Mnemonic FRT3 T3 (Triiodothyronine), Free, Serum

Reporting Name

T3 (Triiodothyronine), Free, S

Useful For

Free triiodothyronine (T3) is a second- or third-level test of thyroid function; it provides further confirmation of hyperthyroidism, supplementing the tetraiodothyronine (T4), sensitive thyrotropin (sTSH), and total T3 assays

 

Evaluating clinically euthyroid patients who have an altered distribution of binding proteins

 

Monitoring thyroid hormone replacement therapy

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type

Serum


Specimen Required


Patient Preparation: For 12 hours before this test do not take multivitamins or dietary supplements containing biotin (vitamin B7), which is commonly found in hair, skin, and nail supplements and multivitamins.

Container/Tube: 

Preferred: Serum gel

Acceptable: Red top

Specimen Volume: 0.6 mL


Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time
Serum Refrigerated (preferred) 7 days
  Frozen  90 days

Reference Values

≥1 year: 2.8-4.4 pg/mL

Day(s) and Time(s) Performed

Monday through Friday; 5 a.m.-12 a.m.

Saturday; 6 a.m.-6 p.m.

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information

84481

LOINC Code Information

Test ID Test Order Name Order LOINC Value
FRT3 T3 (Triiodothyronine), Free, S 3051-0

 

Result ID Test Result Name Result LOINC Value
FRT3C T3 (Triiodothyronine), Free, S 3051-0

Method Name

Immunoenzymatic Assay

Forms

If not ordering electronically, complete, print, and send a General Request Form (T239) with the specimen (http://www.mayomedicallaboratories.com/it-mmfiles/general-request-form.pdf).