T4, Free




Test Mnemonic

FT4

CPT Codes

  • 84439 - QTY (1)

LOINC ®

3024-7

Aliases

  • Thyroxine 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

T4, Free
Sex Age From Age To Type Range Range Unit
   Years5 YearsNormal0.8 - 2.8ng/dL
 6 Years15 YearsNormal0.8 - 2.1ng/dL
 18 Years99 YearsNormal0.9 - 1.7ng/dL
Male16 Years17 YearsNormal0.8 - 2.8ng/dL
Female16 Years17 YearsNormal0.8 - 1.5ng/dL

Special Info

Clinical Info

Thyroxine (T4) is one of the major thyroid hormones, along with triiodothyronine (T3). T4 is the most abundant thyroid hormone, and it regulates metabolism, growth, and development. Free T4 is the active form of thyroxine, and it is generally thought to be more accurate than total T4 for testing for thyroid hormone function because free T4 is not affected by protein levels. Free T4 represents just a fraction of total circulating thyroxine, ranging from 0.03% to 0.05%. Testing for free T4 is commonly ordered in response to an abnormal thyroid-stimulating hormone (TSH) result. An elevated free T4 result is consistent with an overactive thyroid (hyperthyroidism), and a decreased free T4 result is consistent with an underactive thyroid (hypothyroidism). Free T4 may also be used to evaluate thyroid function in patients with alternations in thyroxine binding globulin (TBG).