How is hyperthyroidism diagnosed?

Diagnosing hyperthyroidism is based on history and physical exam findings along with appropriate laboratory testing. On physical exam, the physician may find that the patient has a rapid heart rate (tachycardia), irregular heart beats (arrhythmias, including atrial fibrillation), eye symptoms (such as dryness, burning, bulging, double vision), or hand tremors. In addition, the thyroid gland may be larger than normal. 

Your doctor will ask questions about your medical history, do a physical exam, and order medical tests to diagnose hyperthyroidism.

If your doctor thinks you may have hyperthyroidism, he or she may order:

• A thyroid-stimulating hormone (TSH) test, which is a blood test that measures your levels of TSH. If your TSH level is low, your doctor will want to do more tests.
• Thyroid hormone tests, which are blood tests to measure your levels of two types of thyroid hormones, called T3 and T4. If your thyroid hormone levels are high, you have hyperthyroidism.

When you are being treated for hyperthyroidism, your doctor will test your TSH and thyroid hormones several times a year to see how well your treatment is working.

After you are diagnosed with hyperthyroidism, your doctor may also want to do:

• An antithyroid antibody test to see if you have the kind of antibodies that attack thyroid tissue. This test can help diagnose Graves' disease and autoimmune thyroiditis.
• A radioactive thyroid scan and radioactive iodine uptake tests, which use radiation and a special camera to find out the cause of your hyperthyroidism.

If you have Graves' ophthalmopathy, your doctor may also do an ultrasound, an MRI, or a CT scan to look more closely at your eyes.

Early detection

It is not clear whether people who do not have any risk factors and who do not have any symptoms of hyperthyroidism need to be tested regularly for thyroid problems. The American Thyroid Association recommends that adults, particularly women, be screened for thyroid problems every 5 years, beginning at age 35. The U.S. Preventive Services Task Force does not think there is enough evidence to recommend either for or against regular thyroid testing. Talk to your doctor about whether you need to be tested for thyroid problems.

A patient's history and physical exam are important factors in making the diagnosis of hyperthyroidism. Some patients may have tachycardia (i.e. a rapid heart rate), arrhythmias (i.e. an irregular heart rate such as atrial fibrillation), tremors, thyroid bruit (i.e. a rushing sound in the thyroid when listened to with a stethoscope), a larger than normal thyroid, and eye abnormalities (dryness, bulging eyes, double vision). Blood tests are critical to confirming the diagnosis. Patients with hyperthyroidism will usually have a low TSH and a higher than normal T4 and/or T3 level. In fact, some patients may have no symptoms at all, but blood tests that make the diagnosis of hyperthyroidism.