FT4

Medical abbreviation · Laboratory Test

FT4
Stands forFree thyroxine
CategoriesMedical

FT4 stands for Free thyroxine, a laboratory test abbreviation.

Unbound, active portion of thyroxine (T4), the main hormone secreted by the thyroid, with typical values around 0.8 to 1.8 ng/dL. Paired with TSH, it distinguishes overt from subclinical thyroid disease and is the key monitoring test when pituitary disease makes TSH unreliable.

Example: TSH 0.01 and FT4 3.9: overt hyperthyroidism, uptake scan ordered.

Usage notes

More than 99.9 percent of T4 circulates bound to proteins, mainly thyroxine-binding globulin, so total T4 is distorted by pregnancy, estrogen and liver disease while free T4 is not. Some labs reflex an FT4 automatically when the TSH is abnormal. The SI unit is pmol/L (roughly 10 to 23 pmol/L).

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This entry is for general education and is not medical advice. Abbreviation use varies between institutions; always confirm in context.