Hyperthyroidism is diagnosed using:
- Medical history and physical exam. During the exam your doctor may try to detect a slight tremor in your fingers when they're extended, overactive reflexes, eye changes and warm, moist skin. Your doctor will also examine your thyroid gland as you swallow to see if it's enlarged, bumpy or tender and check your pulse to see if it's rapid.
- Blood tests. A diagnosis can be confirmed with blood tests that measure the levels of thyroxine and TSH in your blood. High levels of thyroxine and low or nonexistent amounts of TSH indicate an overactive thyroid. The amount of TSH is important because it's the hormone that signals your thyroid gland to produce more thyroxine. These tests are particularly necessary for older adults, who may not have classic symptoms of hyperthyroidism.
If blood tests indicate hyperthyroidism, your doctor may recommend one of the following tests to help determine why your thyroid is overactive:
Oct. 28, 2015
Radio iodine uptake test. For this test, you take a small, oral dose of radioactive iodine (radioiodine). Over time, the iodine collects in your thyroid gland because your thyroid uses iodine to manufacture hormones. You'll be checked after two, six or 24 hours — and sometimes after all three time periods — to determine how much iodine your thyroid gland has absorbed.
A high uptake of radioiodine indicates your thyroid gland is producing too much thyroxine. The most likely cause is either Graves' disease or hyperfunctioning nodules. If you have hyperthyroidism and your radioiodine uptake is low, this indicates that the thyroxine stored in the gland is leaking into the bloodstream and indicates you may have thyroiditis.
Knowing what's causing your hyperthyroidism can help your doctor plan the appropriate treatment. A radioactive iodine uptake test isn't uncomfortable, but it does expose you to a small amount of radiation.
Thyroid scan. During this test, you'll have a radioactive isotope injected into the vein on the inside of your elbow or sometimes into a vein in your hand. You then lie on a table with your head stretched backward while a special camera produces an image of your thyroid gland on a computer screen.
The time needed for the procedure may vary, depending on how long it takes the isotope to reach your thyroid gland. You may have some neck discomfort with this test, and you'll be exposed to a small amount of radiation.
Sometimes you may have a thyroid scan as part of a radioactive iodine uptake test. In that case, the orally administered radioactive iodine is used to image your thyroid gland.
- AskMayoExpert. Hyperthyroidism. Rochester, Minn.: Mayo Foundation for Medical Education and Research; 2015.
- Ross DS. Diagnosis of hyperthyroidism. http://www.uptodate.com/home. Accessed Sept. 11, 2015.
- Ross DS. Overview of the clinical manifestations of hyperthyroidism in adults. http://www.uptodate.com/home. Accessed Sept. 11, 2015.
- Ross DS. Disorders that cause hyperthyroidism. http://www.uptodate.com/home. Accessed Sept. 11, 2015.
- Hyperthyroidism. Merck Manual Professional Version. http://www.merckmanuals.com/professional/endocrine-and-metabolic-disorders/thyroid-disorders/hyperthyroidism. Accessed Sept. 11, 2015.
- Tintinalli JE, et al. Thyroid disorders: Hyperthyroidism and thyroid storm. In: Tintinalli's Emergency Medicine: A Comprehensive Study Guide. 7th ed. New York, N.Y.: The McGraw Hill Companies; 2011. http://www.accessmedicine.com. Accessed Sept. 11, 2015.
- Hyperthyroidism. American Thyroid Association. http://www.thyroid.org/what-is-hyperthyroidism/. Accessed Sept. 11, 2015.
- Graves' disease. National Institute of Diabetes and Digestive and Kidney Diseases. http://www.niddk.nih.gov/health-information/health-topics/endocrine/graves-disease/Pages/fact-sheet.aspx. Accessed Sept. 11, 2015.
- Dietary reference intakes for calcium and vitamin D. Institute of Medicine. http://www.iom.edu/vitamind. Accessed July 17, 2012.
- Nippoldt TB (expert opinion). Mayo Clinic, Rochester, Minn. Sept. 18, 2015.