Free T3
Free T3 measures the unbound, active form of triiodothyronine, the most potent thyroid hormone. It helps evaluate thyroid function and diagnose thyroid disorders.
Category: Thyroid Panel
Also known as: free t3, ft3, triiodothyronine free, free triiodothyronine, slobodni t3
Reference range: 2 — 4.4 pg/mL (Source: ABIM)
Standard unit: pg/mL
High values may indicate
High free T3 may indicate hyperthyroidism, Graves' disease, T3 thyrotoxicosis, or early-stage thyroid overactivity.
Low values may indicate
Low free T3 may indicate hypothyroidism, severe non-thyroidal illness (sick euthyroid syndrome), or malnutrition.
Frequently asked questions
- What is a normal Free T3 level?
- A typical reference range for Free T3 is 2 — 4.4 pg/mL (source: ABIM). Reference ranges vary by laboratory, age, and sex, so always compare against the range on your own lab report.
- What units is Free T3 measured in?
- Free T3 is most commonly reported in pg/mL. Labs in different countries may use other units — you can convert between them with BloodId's blood test unit converter.
- Where do Free T3 reference ranges come from?
- BloodId uses ABIM standard reference ranges and educational information from MedlinePlus (see our methodology). Reference ranges still vary by lab, age, and sex, so always compare against your own report.
- Can I track Free T3 over time?
- Yes. Upload results from any lab and BloodId charts your Free T3 over time against its reference range, so you can see whether the trend is rising, falling, or stable.
Related biomarkers
Source: MedlinePlus, U.S. National Library of Medicine