Thyroid function tests are commonly done to see how well the thyroid is working. Some of the most common include:
Blood tests. This test is done to measure the level of thyroid-stimulating hormone (TSH) in the blood. This helps see how well the thyroid is working. High levels of the TSH indicate an underactive thyroid. Very low levels indicate an overactive thyroid.
Ultrasound. This test uses high-frequency sound waves to create an image of the internal organs. It's done to find signs of abnormal enlargement, or nodules, on the thyroid. It's also used to guide biopsies of nodules.
Thyroid scans. This test helps find the cause of abnormal thyroid function. This may be important in deciding whether you will need your thyroid removed (thyroidectomy).
Radioactive iodine uptake test. This test involves giving a small amount of radioactive iodine to measure how much is taken up by the thyroid. This test can tell the difference between several causes of increased thyroid hormone blood levels.