fT3 / fT4 ratio
Stomach and gut healthThe ratio of free triiodothyronine (fT3) to free thyroxine (fT4) reflects how efficiently your body converts the storage thyroid hormone (T4) into the active form (T3).
A low ratio may indicate impaired conversion, which can occur with stress, illness, selenium deficiency, or certain medications — even when individual thyroid values appear normal.
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