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Free T4 Index (T7)
Free T4 Index (FT4I, also called T7) is a calculated estimate of the amount of free thyroxine in your bloodstream. Thyroxine (T4) is a hormone made by the thyroid gland and released into blood mostly attached to carrier proteins (thyroxine‑binding globulin, transthyretin, albumin). At home blood testing is available in select states. See FAQs below
T3 Uptake
T3 uptake is a derived measure from a blood sample that estimates the carrying capacity of the blood for thyroid hormones. It does not measure triiodothyronine itself. Instead, it reflects how many binding sites on the blood’s thyroid hormone carrier proteins are available or already occupied. At home blood testing is available in select states. See FAQs below
Thyroglobulin Antibodies
Thyroglobulin antibodies are immune proteins your body makes that target thyroglobulin, a large protein produced only by thyroid cells. Thyroglobulin (Tg) sits inside the thyroid’s follicles as the scaffold on which thyroid hormones are built. When the immune system becomes misdirected, B cells create antibodies against this self-protein (autoantibodies), which then circulate in the bloodstream. At home blood testing is available in select states. See FAQs below
Thyroid Peroxidase Antibodies (TPO)
Thyroid peroxidase antibody testing looks for immune proteins that target a key thyroid enzyme. Thyroid peroxidase lives on the surface of thyroid hormone–making cells and helps attach iodine to the hormone’s building blocks. When the immune system produces antibodies against this enzyme, they circulate in the blood and can be measured. At home blood testing is available in select states. See FAQs below
Thyroid-Stimulating Hormone (TSH)
Thyroid‑stimulating hormone is the body’s main signal that tells the thyroid what to do. It is made by the front part of the pituitary gland at the base of the brain (anterior pituitary) and released into the bloodstream. This hormone is also called thyrotropin (TSH). At home blood testing is available in select states. See FAQs below
Thyroxine (T4), Total
Thyroxine is the primary hormone produced by the thyroid gland in the neck. A Total T4 blood test measures the full amount of thyroxine in circulation, combining the small fraction that is unbound with the larger fraction attached to carrier proteins (free and protein‑bound T4). At home blood testing is available in select states. See FAQs below
Triiodothyronine (T3), Free
Triiodothyronine (T3) is the body’s most active thyroid hormone. It is produced in small amounts by the thyroid gland and largely formed throughout the body when enzymes remove an iodine atom from thyroxine (T4) in organs like the liver and kidneys (peripheral deiodination). At home blood testing is available in select states. See FAQs below
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