Free Thyroxine Index (T7)
The Free Thyroxine Index (T7) is a calculated estimate of free T4, derived from total T4 and a T3-uptake measurement. It was historically used before direct free T4 testing became routinely available on most lab panels.
Why it matters: Where direct free T4 testing is available, that is generally preferred. T7 still appears on some panels and can give an estimate of free T4 levels when binding-protein conditions affect total T4 readings.
May increase with:
May decrease with:
What is Free Thyroxine Index (T7)?
The Free Thyroxine Index (T7) is a calculated estimate of free T4, derived from total T4 and a T3-uptake measurement. It was historically used before direct free T4 testing became routinely available on most lab panels.
What might a high or low Free Thyroxine Index (T7) mean?
Where direct free T4 testing is available, that is generally preferred. T7 still appears on some panels and can give an estimate of free T4 levels when binding-protein conditions affect total T4 readings.
What can affect Free Thyroxine Index (T7)?
It may be higher with: Hyperthyroidism, TBG elevation. It may be lower with: Hypothyroidism, TBG reduction.
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