T3 is the only hormone that your body can actually use, so your body must first convert T4 to T3. An enzyme called deiodinase does this by removing one iodine molecule.
T3 helps control your body’s metabolism — the chemical processes that occur in your body that keep you alive, like breathing and breaking down food into energy.
Sometimes, your thyroid gland might produce too much or too little T3 and T4. If you don’t produce enough it’s called hypothyroidism (an underactive thyroid) and if you produce too much it’s called hyperthyroidism (an overactive thyroid).
It’s important to test your thyroid if you think you might suffer from a thyroid disorder.
If left untreated, an underactive thyroid can cause:
If left untreated, an overactive thyroid can cause:
Thyroid disorders are also associated with pregnancy complications, like miscarriage, premature birth, and pre-eclampsia.
You can check for a thyroid disorder with a blood test.
A basic test will check your thyroid hormone levels, which can diagnose an underactive or overactive thyroid. A more advanced test will also check for thyroid antibodies, called thyroid peroxidase antibody (TPO) and thyroglobulin antibody (TGAb). These antibodies are what cause autoimmune thyroid diseases.
An underactive thyroid is usually treated with a medication called levothyroxine — a hormone replacement tablet.
An overactive thyroid is usually treated with either medication, radiation, or surgery.
American Thyroid Association and American Association of Clinical Endocrinologists Taskforce on Hyperthyroidism and Other Causes of Thyrotoxicosis, Bahn, R. S., Burch, H. B., Cooper, D. S., Garber, J. R., Greenlee, M. C., ... & Rivkees, S. A. (2011). Hyperthyroidism and other causes of thyrotoxicosis: management guidelines of the American Thyroid Association and American Association of Clinical Endocrinologists. Thyroid, 21(6), 593-646.
Abalovich, M., Amino, N., Barbour, L. A., Cobin, R. H., De Groot, L. J., Glinoer, D., ... & Stagnaro-Green, A. (2007). Management of thyroid dysfunction during pregnancy and postpartum: an Endocrine Society Clinical Practice Guideline. The Journal of Clinical Endocrinology & Metabolism, 92(8_supplement), s1-s7.
Casey, B. M., Dashe, J. S., Wells, C. E., McIntire, D. D., Byrd, W., Leveno, K. J., & Cunningham, F. G. (2005). Subclinical hypothyroidism and pregnancy outcomes. Obstetrics & Gynecology, 105(2), 239-245.
Garber, J. R., Cobin, R. H., Gharib, H., Hennessey, J. V., Klein, I., Mechanick, J. I., ... & Woeber for the American Association of Clinical Endocrinologists and American Thyroid Association Taskforce on Hypothyroidism in Adults, K. A. (2012). Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association. Thyroid, 22(12), 1200-1235.