T3, Free




Test Mnemonic

FREET3

CPT Codes

  • 84481 - QTY (1)

LOINC ®

3051-0

Aliases

  • Triiodothyronine, Free

Performing Laboratory

n/a


Specimen Requirements

Volume Type Container Collect Temperature Transport Temperature Special Instructions
1 mLPlasmaLithium heparin PST (Lt. Green) Centrifuge and refrigerate.Submit in original tube or aliquot into CCL aliquot tube

Alternate Specimen Requirements

Volume Type Container Collect Temperature Transport Temperature Special Instructions
1 mLSerumSST (Gold) Centrifuge and refrigerate. 

Minimum Specimen Requirements

Volume Type Container Collect Temperature Transport Temperature Special Instructions
0.5 mL     

Stability

Environmental Condition Description
Ambient5 days
Refrigerated7 days
Frozen30 days

Days Performed

Sun - Sat

Turnaround Time

8 hours

Methodology

Name Description
Electro Chemiluminescence Immunoassay (ECLIA) 

Reference Range

T3, Free
Sex Age From Age To Type Range Range Unit
   Days3 DaysNormal1.4 - 5.4pg/mL
 4 Days30 DaysNormal2.0 - 5.2pg/mL
 31 Days364 DaysNormal1.5 - 6.4pg/mL
 1 Years6 YearsNormal2.0 - 6.0pg/mL
 7 Years11 YearsNormal2.7 - 5.2pg/mL
 12 Years17 YearsNormal2.3 - 5.0pg/mL
 18 Years99 YearsNormal2.3 - 4.1pg/mL

Special Info

Clinical Info

Triiodothyronine (T3) is one of the major thyroid hormones, along with thyroxine (T4). T3 has greater biological activity than T4 and is considered the metabolically active form of thyroid hormone. The activity of T3 is directly regulated by thyroxine binding globulin (TBG), but T3 binds less strongly to TBG than T4. Free T3 represents just a fraction of total circulating T3 (about 0.3%), but free T3 is not affected by protein levels. This assay is usually ordered to diagnose a type of hyperthyroidism known as thyrotoxicosis. In thyrotoxicosis, T3 values are high while T4 (total or free) is normal and TSH is low. Decreased T3 levels occur in drug therapy with androgens, prednisone, dexamethasone, and glucocorticoids. Decreased T3 levels also occur in iodine deficiency, non-thyroidal disease also known as low T3 syndrome, anorexia nervosa, and following surgery to remove the thyroid gland.