Other Blood Tests
Healthcare providers may conduct additional tests to help confirm a hypothyroidism diagnosis or determine the cause.
The T4 test measures the actual amount of circulating thyroid hormone in the blood. In hypothyroidism, the level of T4 in the blood is lower than normal.
Another test looks for the presence of thyroid autoantibodies. Most people with Hashimoto's thyroiditis (the most common cause of hypothyroidism) have these antibodies, but people whose hypothyroidism is caused by other conditions do not.