Free T3
Tri-iodothyronine (T3) is one of the main thyroid hormones that help control energy levels, metabolism, and body temperature. The Free T3 Test measures the amount of active (unbound) T3 circulating in the blood, providing a more accurate picture of how well your thyroid is working. This test is often used to help diagnose hyperthyroidism (overactive thyroid), hypothyroidism (underactive thyroid), and other thyroid-related conditions. It’s also useful for people experiencing symptoms like unexplained weight changes, fatigue, heart palpitations, or mood swings, and for monitoring T3 treatment.
Test details
Sample type
Blood
Time of day
No Specific Time Needed
Fasting required
No
Results timeframe
Within 7 days
Preparation
No special preparation required.
What's measured in this test
Free T3
Active thyroid hormone for energy and metabolism.
Common reasons for testing
- Unexplained weight gain or loss – Checks whether thyroid imbalances are affecting metabolism.
- Fatigue or low energy levels – Helps assess thyroid function as a possible cause of ongoing tiredness.
- Heart palpitations or anxiety – Identifies high T3 levels, which can be linked to hyperthyroidism.
- Thyroid disease monitoring – Tracks thyroid hormone levels in individuals on treatment for thyroid disorders.
- Cold intolerance or overheating – Evaluates whether thyroid function is affecting body temperature regulation.
- Mood changes or brain fog – Assesses if thyroid hormone imbalances are contributing to depression, anxiety, or trouble concentrating.
- What This Test Checks For
- This test measures free T3, which is the active form of the thyroid hormone that directly affects metabolism and energy levels.