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How is Graves' disease diagnosed?

Doctors can sometimes diagnose Graves' disease only on the basis of a physical examination and a medical history. Laboratory tests confirm the diagnosis.

The ultra-sensitive thyroid-stimulating hormone (TSH) test is usually the first test a doctor performs. This test detects even tiny amounts of TSH in blood and is the most accurate measure of thyroid activity available. Another blood test used to diagnose Graves' disease measures triiodothyronine (T3) and thyroxine (T4). In making a diagnosis, doctors 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, doctors may order other tests to finalize the diagnosis. Two of these tests are based on the fact that the thyroid gland uses iodine to make thyroid hormone. Both tests use small, safe doses of radioactive iodine.

The radioactive iodine uptake test measures the amount of iodine the thyroid collects from the bloodstream. High levels of iodine uptake can indicate Graves' disease. A thyroid scan shows how and where iodine is distributed in the thyroid. In Graves' disease, the entire thyroid gland is involved. So, the iodine shows up throughout the gland. Other causes of hyperthyroidism such as nodules-small lumps in the gland-will show a different pattern of iodine distribution.

Doctors may also consider the thyroid-stimulating immunoglobulin (TSI) test, although this test usually isn't necessary to diagnose Graves' disease. This test, also called a TSH antibody test, measures the level of TSI in blood. Most people with Graves' disease have this antibody, but people whose hyperthyroidism is caused by other conditions do not have this antibody.

This information is based on source information from the National Institute of Diabetes and Digestive and Kidney Diseases.

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