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Free T3

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Free triiodothyronine (T3) is a measure of the amount of T3 that is not protein bound. Most T3 is protein bound, mainly to thyroxine-binding globulin. The unbound portion is the active part.

The normal range for free T3 is 3-9 pmol per litre. It's measurement may be useful if a false high or low T3 is suspected.

Note that reference ranges may vary between laboratories.

Reference

  1. Thyroid Function Tests. British Thyroid Foundation, revised 2021

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