In order to perform a healthy rate of metabolism that is needed by the body, the thyroid gland produces the T3 (triiodothyronine) and T4 (thyroxine) hormones. When the body uses these hormones, the thyroid creates more to replace them. The pituitary gland monitors the amount of the thyroid hormones in the bloodstream and adjusts the production of its own hormone accordingly. The pituitary gland also sends this information to the thyroid gland so the latter knows how much hormone it needs to produce (Endocrine Web, 2006a) Thyroid diseases occur when the thyroid gland produces more hormones, which prompts the body to consume more energy. This disorder is called hyperthyroidism. When the thyroid gland produces fewer hormones, the body is prompted to lessen its energy consumption. This condition is called hypothyroidism. The symptoms of hyperthyroidism include severe irritability and nervousness, muscle tremors, unpredictable and infrequent menstrual periods in women, sudden weight loss, inability to sleep, enlarged thyroid, eye irritation, and sensitivity to heat. The symptoms of hypothyroidism are fatigue, heavy and frequent menstrual periods in women, severe forgetfulness, sudden weight gain, dry hair and skin, raspy voice, and sensitivity to cold. Doctors perform various thyroid diagnostic tests to determine if the thyroid gland is functioning well. These tests include the T3 and T4 tests, the TSH (thyroid stimulating hormone) test, and ultrasound of the thyroid gland. The TSH test is usually done first, as it is the best measure of how well the thyroid gland functions.