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Test ID: FRT3P    
T3 (Triiodothyronine), Free and Total, 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

Triiodothyronine (T3) is a second-order test in follow-up to low thyroid stimulating hormone values in the evaluation of patients suspected of having hyperthyroidism caused by excess T3 (T3 toxicosis).


Free T3 (FT3) levels can be helpful in evaluating patients with altered levels of binding proteins, such as pregnant patients, patients receiving estrogens and anabolic steroids, and patients with dysalbuminemia. Some investigators recommend FT3 for monitoring thyroid replacement therapy, although its clinical role is not precisely defined. FT3 also provides a further confirmatory test for hyperthyroidism to supplement the thyroxine (T4), sensitive thyrotropin, and total T3 assays.

Profile Information A profile is a group of laboratory tests that are ordered and performed together under a single Mayo Test ID. Profile information lists the test performed, inclusive of the test fee, when a profile is ordered and includes reporting names and individual availability.

Test IDReporting NameAvailable SeparatelyAlways Performed
FRT3T3 (Triiodothyronine), Free, SYesYes
T3T3 (Triiodothyronine), Total, SYesYes

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

FRT3: Immunoenzymatic Assay

T3: Electrochemiluminescence Immunoassay

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

T3 (Triiodothyronine), Fr + Tot, S

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

Free & Total T3, Serum
FT3 and TT3
T3, Free & Total, Serum
Total & Free T3, Serum