Thyroid
The hormones that set your metabolic pace, and antibodies that can attack the thyroid.
13 tests explained
Most common tests
- Free T3 (Free Triiodothyronine)The unattached, active form of the thyroid hormone T3, which drives how fast your cells use energy. It is usually checked after TSH and free T4.
- Free T4 (Free Thyroxine)The unattached, ready-to-use part of thyroxine (T4), the main hormone your thyroid makes. It shows how much thyroid hormone is available to your body.
- Thyroid Peroxidase Antibodies (TPO)Antibodies aimed at an enzyme in the thyroid. They are linked to autoimmune thyroid conditions such as Hashimoto's thyroiditis.
- TSH (Thyroid Stimulating Hormone)A hormone from the pituitary gland that tells your thyroid how much hormone to make. It is the test most often ordered first to check your thyroid.
Common follow-up tests
- Free Thyroxine Index (T7)A calculated estimate of how much active thyroxine (T4) is available, worked out from total T4 and T3 uptake. It is an older alternative to measuring free T4.
- Reverse T3An inactive by-product of thyroxine (T4). Its usefulness is limited, and an American Thyroid Association review says routine testing is not needed.
- T3 UptakeShows how many binding spots on your blood proteins are open for thyroid hormone. It is not a hormone level, and it is used to work out the free thyroxine index.
- Thyroglobulin (Tg)A protein made only by thyroid cells. It is mainly used after thyroid cancer treatment as a tumor marker, and it is not a test for diagnosing cancer.
- Thyroglobulin AntibodiesAntibodies aimed at thyroglobulin, a protein made in the thyroid. They are linked to autoimmune thyroid conditions and affect thyroglobulin testing.
- Thyroid Stimulating Immunoglobulin (TSI)Antibodies that stimulate the thyroid by acting like TSH. A positive result is strongly linked to Graves' disease.
- Total T3 (Triiodothyronine)Measures all the T3 in your blood, the more active thyroid hormone, including the part attached to carrier proteins.
- Total T4 (Thyroxine)Measures all the thyroid hormone thyroxine in your blood, both the part attached to carrier proteins and the small free part.
- TSH Receptor Antibodies (TRAb / TBII)Antibodies that attach to the thyroid's TSH receptor. They are strongly linked to Graves' disease, an autoimmune cause of an overactive thyroid.