Understanding Triiodothyronine – Free (FT3)
At Curis Life Clinic, the Triiodothyronine – Free (FT3) test helps assess your thyroid gland’s activity and overall metabolic health. The thyroid, a small butterfly-shaped gland in the neck, produces vital hormones—chief among them triiodothyronine (T3)—that regulate metabolism, body temperature, heart rate, red blood cell production, tissue development, and brain function.
T3 exists in two forms in the bloodstream:
- Free T3 – the unbound, active form that directly affects body functions.
- Bound T3 – the inactive form attached to proteins in the blood.
The FT3 test measures only the free form of T3, offering a more accurate reflection of thyroid hormone activity in the body. Abnormal FT3 levels may indicate thyroid disorders such as:
- Hyperthyroidism: when the thyroid produces excess hormone.
- Hypothyroidism: when the thyroid produces insufficient hormone.
Doctors at Curis Life may recommend this test if you experience symptoms such as:
- Hyperthyroidism: weight loss, increased appetite, anxiety, tremors, sweating, or palpitations.
- Hypothyroidism: fatigue, weight gain, dry skin, constipation, or sensitivity to cold.
This test also helps evaluate how well thyroid medications are working and detect abnormalities in thyroid-binding proteins.
Preparation Required
No special preparation is needed before the FT3 test. You may eat and drink as usual. However, inform your doctor about all medications and supplements, as certain ones (like Biotin or Vitamin B7) may interfere with results. It’s recommended to avoid biotin for two days before testing.
Test Interpretation
FT3 results can vary across laboratories depending on testing methods. Always discuss your results with your doctor rather than self-diagnosing. Your Curis Life doctor will help interpret your levels, recommend diet or lifestyle modifications, and decide if medical treatment is necessary.
What Does Triiodothyronine – Free (FT3) Measure?
The Triiodothyronine – Free (FT3) test measures the concentration of unbound (free) T3 hormone circulating in your blood. This active hormone regulates metabolism, energy use, and tissue growth.
While most T3 binds to proteins like albumin and thyroid-binding globulin (TBG), only the free form is biologically active. By measuring FT3, doctors can assess how efficiently your thyroid is functioning and detect thyroid disorders early for timely management.
