Free T4
Thyroxine (T4) is one of the main thyroid hormones that helps regulate metabolism, energy levels, and body temperature. The Free T4 Test measures the amount of active (unbound) T4 in the blood, giving a clear picture of how well your thyroid is working. This test is often used to diagnose hypothyroidism (underactive thyroid), hyperthyroidism (overactive thyroid), and other thyroid-related conditions. It’s useful for people experiencing symptoms like fatigue, weight changes, dry skin, hair thinning, or mood swings.
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 T4
Inactive thyroid hormone affecting metabolism.
Common reasons for testing
- Unexplained weight gain or loss – Checks if thyroid imbalances are affecting metabolism.
- Fatigue or low energy levels – Assesses whether thyroid hormone levels are contributing to ongoing tiredness.
- Thyroid disease diagnosis – Helps detect hypothyroidism or hyperthyroidism.
- Thyroid treatment monitoring – Tracks T4 levels for individuals on thyroid hormone replacement or other thyroid treatments.
- Hair thinning, dry skin, or temperature changes – Evaluates whether thyroid function is affecting skin, hair, and body temperature regulation.
- Mood changes or brain fog – Checks if thyroid hormone imbalances may be contributing to depression, anxiety, or trouble focusing.
- What This Test Checks For
- This test measures free T4, the active form of thyroxine, which directly affects metabolism and energy levels.