How to diagnose Graves' Disease ?
Health care providers can sometimes diagnose Graves disease based only on a physical examination and a medical history. Blood tests and other diagnostic tests, such as the following, then confirm the diagnosis.
                
TSH test. The ultrasensitive TSH test is usually the first test performed. This test detects even tiny amounts of TSH in the blood and is the most accurate measure of thyroid activity available.
                
T3 and T4 test. Another blood test used to diagnose Graves disease measures T3 and T4 levels. In making a diagnosis, health care providers look for below-normal levels of TSH, normal to elevated levels of T4, and elevated levels of T3.
                
Because the combination of low TSH and high T3 and T4 can occur with other thyroid problems, health care providers may order other tests to finalize the diagnosis. The following two tests use small, safe doses of radioactive iodine because the thyroid uses iodine to make thyroid hormone.
                
Radioactive iodine uptake test. This test measures the amount of iodine the thyroid collects from the bloodstream. High levels of iodine uptake can indicate Graves disease.
                
Thyroid scan. This scan shows how and where iodine is distributed in the thyroid. With Graves disease the entire thyroid is involved, so the iodine shows up throughout the gland. Other causes of hyperthyroidism such as nodulessmall lumps in the glandshow a different pattern of iodine distribution.
                
TSI test. Health care providers may also recommend the TSI test, although this test usually isnt necessary to diagnose Graves disease. This test, also called a TSH antibody test, measures the level of TSI in the blood. Most people with Graves disease have this antibody, but people whose hyperthyroidism is caused by other conditions do not.
                
More information about testing for thyroid problems is provided in the NIDDK health topic, Thyroid Tests.