Thyroid hormone tests are done to: 1  Find out what is causing an abnormal thyroid-stimulating hormone (TSH) test. 2  Check how well treatment of thyroid disease is working. 3  Screen newborns to find out if the thyroid gland function is normal.hy It Is Done. Thyroid hormone tests are done to: 1  Find out what is causing an abnormal thyroid-stimulating hormone (TSH) test. 2  For more information, see the topic Thyroid-Stimulating Hormone (TSH) . 3  This is the most common reason for thyroid hormone tests.