Although Graves' disease can be diagnosed from the results of one or two tests, your doctor may use several methods to double-check the findings and rule out other disorders. An analysis of your blood will show if the levels of two hormones -- free thyroxine (free T-4) and triiodothyronine (free T-3), which are produced or regulated by the thyroid -- are higher than normal. If they are, and if levels of thyroid-stimulating hormone (TSH) in your blood are abnormally low, you are hyperthyroid, and Graves' disease is the likely culprit. Blood analysis can also detect the presence of the abnormal antibody associated with Graves' disease.
To confirm a diagnosis of Graves' disease, your doctor may do a radioactive iodine uptake test, which shows whether large quantities of iodine are collecting in the thyroid. The gland needs iodine to make thyroid hormones, so if it's absorbing unusually large amounts of iodine, it's obviously making too much hormone.
If bulging eyeballs (called exophthalmos) is the only symptom, your doctor will probably run blood tests to check for hyperthyroidism, since this eye disorder is not always related to Graves' disease. The doctor may also evaluate eye muscles using ultrasound, a CT scan, or magnetic resonance imaging (MRI). Signs of swelling in any one of these tests will go along with the diagnosis of Graves' disease.