Free Triiodothyronine (fT3)

Active thyroid hormone at the tissue level. Useful in suspected T3-toxicosis.

Units

pg/mL

Reference (Male)

2.3 – 4.2 pg/mL

Reference (Female)

2.3 – 4.2 pg/mL

Aliases

Free T3

What it measures

Active thyroid hormone at the tissue level. Useful in suspected T3-toxicosis.

What a high value can mean

Hyperthyroidism, T3 toxicosis.

What a low value can mean

Hypothyroidism, severe systemic illness (non-thyroidal illness syndrome).

Conditions it helps assess

Active thyroid hormone level

Reading these numbers in context

Reference ranges describe the central 95 % of a healthy reference population — 5 % of perfectly healthy people fall outside any given range by definition. A single mildly abnormal value is rarely meaningful on its own. blood-test.life always interprets values together with related biomarkers before flagging.

Related biomarkers in Thyroid Panel

Thyroid-Stimulating Hormone TSH Pituitary hormone that controls thyroid output. The most sensitive screen for thyroid dysfunction. Free Thyroxine fT4 Active, unbound form of T4. Distinguishes primary from central thyroid disease.