The thyroid gland is responsible for multiple functions of the body. When the functions are interrupted, various ailments can be experienced. Thyroid function test helps in identifying the problems with the thyroid gland. The underactive thyroid, also known as, hypothyroidism, and overactive thyroid, also known as hyperthyroidism can be determined using this thyroid test. This is a blood test, which checks the level of thyroid hormone made by the pituitary gland.