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Test ID: FRT4    
T4 (Thyroxine), Free, Serum

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Secondary ID A test code used for billing and in test definitions created prior to November 2011


NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.


Useful For Suggests clinical disorders or settings where the test may be helpful

The test generally is used as a second-line test after thyroid-stimulating hormone (TSH) to help evaluate TSH changes.


The free thyroxine value, combined with the TSH value, gives a more accurate picture of the thyroid status in patients with abnormal thyroid-binding globulin levels such as those who are pregnant or those who are receiving treatment with estrogens, androgens, phenytoin, or salicylates.

Testing Algorithm Delineates situation(s) when tests are added to the initial order. This includes reflex and additional tests.

See Thyroid Function Ordering Algorithm in Special Instructions.

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test

Method Name A short description of the method used to perform the test

Chemiluminometric Immunoassay

Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name

T4 (Thyroxine), Free, S

Aliases Lists additional common names for a test, as an aid in searching

Free T4 (Thyroxine)
Free Thyroxine
FT4, Serum
Non-Protein Bound Tetraiodothyronine
T4 Free, Serum
Thyroid Function Cascade ORDER 80683
Thyroxine, Free