When evaluating a patient with suspected thyroid dysfunction, serum TSH concentration should be the initial screening test. If the TSH is low or low to normal, elevations in peripheral serum thyroid hormone levels can help confirm the diagnosis of hyperthyroidism. Subsequently, a 24-hour thyroid RAIU and scan can be ordered to determine the cause of the hyperthyroidism. Serum T3 and T4 levels should not be used as an initial diagnostic test. Thyroid-stimulating immunoglobulin elevations may be seen in patients with Graves disease, but this test is very insensitive.