Free T3 test
Informed by recognized medical guidance
Overview
The Free T3 test is a blood test that measures the amount of free triiodothyronine (free T3) in your blood. T3 is a thyroid hormone that helps control your body's energy use, heart rate, and body temperature. 'Free' means the T3 that is not attached to proteins and is available for your cells to use directly. This test is often done along with other thyroid tests like TSH (thyroid-stimulating hormone) and Free T4 to check how well your thyroid gland is working.
Key facts
- Free T3 is the active form of thyroid hormone that your body can use right away.
- This test helps diagnose conditions such as hyperthyroidism (overactive thyroid) or hypothyroidism (underactive thyroid).
- It is usually ordered if your TSH or Free T4 results are abnormal, or if you have symptoms of a thyroid problem.
Yes, the Free T3 test is a common part of evaluating thyroid function, especially when other thyroid tests are unclear or when symptoms point to a thyroid issue.
It affects people who have symptoms of thyroid disease, those being treated for thyroid conditions, and sometimes people with unexplained weight changes, fatigue, or heart rhythm problems. It can affect people of any age, but thyroid problems are more common in women.