What are thyroid function tests?

Thyroid function tests are common procedures done to determine how well the thyroid is functioning. Some of the most common thyroid function tests include the following:

• Blood tests. This test is done to measure the level of thyroid-stimulating hormone (TSH) in the blood which helps determine thyroid function. High levels of the hormone indicate an underactive thyroid. In addition, a blood test can measure levels of hormones thyroxine (T4) and triiodothyronine (T3), and less often, a protein called thyroglobulin.

• Ultrasound exam of the thyroid gland. An ultrasound scan is a diagnostic technique that uses high-frequency sound waves to create an image of the internal organs. It's done to detect signs of abnormal enlargement, or nodules, on the thyroid, and to guide biopsies of concerning nodules. 

• Thyroid scans using radioactive iodine or technetium (another radioactive element). This test helps determine the cause of abnormal thyroid function. This may be important in deciding whether a person will need a total thyroidectomy or partial thyroidectomy.