T3 (Triiodothyronine)

This test measures the level of triiodothyronine (T3) in the blood. T3 is one of the two main hormones produced by the thyroid gland, and it is the biologically active form that influences how quickly your cells use energy. While the thyroid produces a smaller amount of T3 directly, most T3 is created when the body converts thyroxine (T4) into T3 in the liver and other tissues. Measuring T3 helps build a picture of thyroid function, particularly when total thyroid hormone levels or thyroid-stimulating hormone (TSH) results are abnormal, or when an overactive thyroid is suspected.

The test is suitable for anyone experiencing symptoms that may point to a thyroid imbalance, such as unexplained weight change, palpitations, heat intolerance, anxiety, fatigue, or hair thinning. It is also used to monitor people who are already receiving treatment for a thyroid condition, or to investigate an enlarged thyroid gland. A simple blood sample is all that is required, and the analysis is carried out using a validated immunoassay technique in our laboratory.

Biomarkers included

Thyroid Hormones
- Triiodothyronine (T3)

Why it matters
T3 is the hormone that directly switches on metabolic activity in nearly every cell of the body. When T3 is too high, it can drive symptoms such as a racing heart, weight loss, irritability, and difficulty sleeping. When it is too low, it can contribute to fatigue, weight gain, cold intolerance, and low mood. Because T3 works alongside T4 and TSH, measuring it gives a more complete view of thyroid health than TSH alone, and it can reveal patterns that would otherwise be missed. Clear, accurate T3 results help you and your doctor decide whether further investigation or treatment is needed, and they provide a reliable baseline for tracking any changes over time.