Free T3 (Free Triiodothyronine)
Free T3 is the most active thyroid hormone, formed from T4 in tissues. It regulates metabolism, heart rate, and body temperature.
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Normal ranges
Adults: 2.6–5.7 pmol/L.
Units: pmol/L
Causes of deviations
Low levels:
Hypothyroidism, severe illness, iodine deficiency.
High levels:
Hyperthyroidism, T3-toxicosis, thyroid hormone overdose.
When to see a doctor
If abnormal with palpitations, weight change, or tremor — endocrinologist.
Related biomarkers
Panels
Thyroid panel
Conditions
Hyperthyroidism
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