Free T3

What is Free T3?

T3, or triiodothyronine, is the main active thyroid hormone in the human body. Once released into the bloodstream, TSH is responsible for stimulating the thyroid gland to produce hormones T4 (thyroxine) and T3 (triiodothyronine). T4 is inactive and is converted to the active T3 form, accounting for 80% of total T3 synthesis. While bound T3 (attached to proteins) is unable to enter and act on the body's tissues, free T3 is able to enter tissues and act more readily. 

Why is it included in Thyroid+?

Tracking your free T3 levels allows you to understand the health of your thyroid gland, which is an integral part of your endocrine system. Thyroid hormones are vital to metabolism, heart and digestive functions, muscle control, brain development, and bone maintenance, among other roles. Because of its significance, free T3 is included in SiPhox Health's Thyroid+ panel.

High free T3 may point to hyperthyroidism (overactive thyroid gland), which can be caused by autoimmune diseases or thyroid gland inflammation (thyroiditis). Low free T3 may point to hypothyroidism (underactive thyroid gland). Symptoms of hyperthyroidism may include weight loss, rapid or irregular heartbeat, increased hunger,  and anxiousness among other issues. Symptoms of hypothyroidism on the other hand may include lethargy, weight gain, sensitivity to cold, thinning hair, constipation, and other physical and mental issues. If you are concerned with your levels, it is important to consult with your physician.

How can I better understand my results?

According to the American Board of Internal Medicine, normal levels of free T3 are around 2.3 - 4.2 pg/mL. Free T3 test results are analyzed in conjunction with other thyroid tests to determine whether the thyroid gland is functioning properly.

Like many hormones, T3 follows a circadian rhythm related to the cycles of TSH and T4. Free T3 is generally at its highest concentration at around 4am and at its lowest concentration at around 4pm. As such, testing in the morning compared to in the afternoon may help detect hypothyroidism in individuals who would otherwise appear normal due to rhythmic fluctuation.

If your T3 levels are high, you can try:

If your T3 levels are low, you can try:

Where can I learn more?

MedlinePlus - T3 test

Level Up RN (video) - TSH and T3/T4 - What's the difference?