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2288 pages added, reviewed or updated during the last month (last updated: 20/4/2021)


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T4 (free)

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Free thyroxine (T4) is a measure of the amount of T4 that is not protein bound. Most T4 is protein bound, mainly to thyroxine-binding globulin. The unbound portion is the active part.

The normal range for free T4 is 9-25 pmol per litre. Its measurement is useful when a false high or false low T4 or T3 is suspected.

Note that reference ranges may vary between laboratories.

Last reviewed 01/2018

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