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.