The Triiodothyronine Free (FT3) test measures the level of free T3 in the blood. T3 (triiodothyronine) is a thyroid hormone that plays a key role in metabolism, energy production, and overall thyroid function. The free T3 test specifically measures the active, unbound form of T3, which is available for the body to use.

Why is the FT3 test done?

1. To evaluate thyroid function – Helps assess hyperthyroidism or hypothyroidism.
2. To diagnose and monitor thyroid disorders – Such as Graves’ disease or Hashimoto’s thyroiditis.
3. To check the effectiveness of thyroid medications – Especially for those on thyroid hormone replacement therapy.
4. To investigate symptoms like:
   • Weight changes
   • Fatigue or weakness
   • Heart palpitations
   • Anxiety or depression
   • Heat or cold intolerance

Normal Range of Free T3 (FT3)

• Adults: 2.0 – 4.4 pg/mL (varies slightly by lab)
• Low FT3: May indicate hypothyroidism, starvation, or chronic illness.
• High FT3: Often seen in hyperthyroidism or thyroid hormone resistance.

What do abnormal Free T3 levels mean?

✅ High Free T3 (Hyperthyroidism)

• Graves’ disease
• Toxic multinodular goiter
• Thyroiditis (early phase)
• Excess thyroid medication
• High iodine intake
• Rare: T3-predominant hyperthyroidism

❌ Low Free T3 (Hypothyroidism)

• Hashimoto’s thyroiditis
• Severe iodine deficiency
• Pituitary disorders (low TSH)
• Chronic illness or malnutrition
• Liver disease (since T3 is converted in the liver)

How is the test done?

• A blood sample is taken from a vein.
• No fasting is usually required.
• Results are typically available in 24-48 hours.