Thyroid
Free T4
Also known as: free thyroxine, FT4
What it is
Free T4 is the unbound, available form of thyroxine, the main hormone the thyroid produces. It is typically measured together with TSH to build a fuller picture of thyroid function.
Why it matters
TSH is the first-line screen; free T4 helps clarify what an abnormal TSH means (for example, distinguishing the type or degree of an under- or over-active thyroid). The two are almost always interpreted together.
What “optimal” looks like
A healthy range applies, and free T4 is read in tandem with TSH rather than on its own. Illness and some medications can shift it, so context matters.
This is general information, not medical advice or a diagnosis. Always discuss your results with a qualified clinician.
Related
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