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Thyroid

Free T4

Your laboratory may print this as FT4, Free thyroxine. Usually reported in ng/dL.

On your report

NameFree T4
Also printed asFT4 · Free thyroxine
Usual unitng/dL
Reference rangePrinted by your own laboratory. We publish none of our own.

Comparing two results

A change under about 13.3% may be nothing at all

Free T4 varies within the same healthy person from day to day — for this value, by about 4.8%. So two results can differ without anything having changed. Below roughly 13.3%, a difference is as likely to be ordinary variation as anything else.

This figure is a lower bound, deliberately. The full calculation also includes the variation of the specific machine that ran your sample, which belongs to your laboratory and differs between them. Leaving it out makes the threshold smaller, so this flags changes that may turn out to be nothing — rather than missing ones that matter.

Biological variation figure from the EFLM BVD meta-analysis. Calculated as 2.77 × CVI.

What MedicaCare AI does with this value

Photograph the report and you get your own free t4 explained against the range your laboratory printed — plus every other value on the page, and somewhere to ask what you actually want to know.

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Usually printed alongside it

TSHFree T3