The cause of the thyroid dysfunction may be clinically apparent (for example, the eye signs of Graves' disease). Serological tests may be required to confirm the presence of autoimmune thyroid disease. With the availability of sensitive TSH assays that are capable of recognising low TSH levels, it is rarely necessary to resort to using a thyrotrophin-releasing hormone (TRH) test. It should be noted that a low TSH level alone is not sufficient to establish a diagnosis of hyperthyroidism, since low TSH levels are seen in occasional normal subjects and in some individuals with severe non thyroidal illness.
