Free Thyroxine Index (FTI), Serum
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
T-Uptake (TU) and total thyroxine (T4) are used to estimate the amount of circulating free T4. The estimate, or the free thyroxine index (FTI), is a normalized measurement that remains relatively constant in healthy individuals and compensates for abnormal levels of binding proteins. Hyperthyroidism causes increased FTI and hypothyroidism causes decreased values. TU results are changed by drugs or physical conditions that alter the patient's thyroxine-binding globulin levels, or drugs that compete with endogenous T4 and triiodothyronine (T3) for protein-binding sites. When serum contains high levels of T3 and T4 as in hyperthyroidism, fewer unoccupied binding sites are available. Conversely, in hypothyroidism, more binding sites are available.
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Free Thyroxine Index (FTI), S