Your doctor will ask you about your symptoms and medical/family history, perform a physical exam, and order certain tests. Symptoms that could indicate hyperthyroidism include nervousness, weight loss, heat intolerance, or excessive diarrhea. The physical exam can reveal an enlarged thyroid gland (goiter), bulging eyes, increased reflexes, a fine tremor of the hands, and a rapid pulse.

Tests may include:

Blood Tests —These tests measure the blood levels of thyroid hormones. If the serum level of TSH (thyroid stimulating hormone) is decreased, and serum free T3, free T4, and free T4 index T3 are elevated, this usually means the thyroid gland is too active. Your blood may also be examined for thyroid antibodies, especially if you are pregnant.

Radioiodine Uptake —This test is used to define the cause of hyperthyroidism. The thyroid gland uses iodine to make thyroid hormone. For this test, you will ingest radioactive iodine orally. Some of it is taken up by the thyroid gland. The amount of radioactivity is then measured by a radiation counter over the thyroid. In Graves’ disease , the amount is elevated. This test is not done on children or pregnant women.

Thyroid Scan —This test is used to help differentiate between Graves’ disease and other causes of hyperthyroidism. Radioactive iodine, radio-labeled technetium, or another radioactive substance is used. A scan of the thyroid then gives an idea of the size and shape of the thyroid; it can also show thyroid nodules. A thyroid nodule may or may not be functioning and is termed a “hot” or “cold” nodule. If it is “hot” it can cause hyperthyroidism.

Needle Biopsy —Occasionally, a needle biopsy of the thyroid is needed. A sample of thyroid tissue is removed with a needle and then examined under the microscope. You will be given a local anesthetic for this procedure.