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I-131 for Hyperthyroidism

Diagnosis and Treatment for Hyperthyroidism

Diagnosis of hyperthyroidism

If your healthcare provider suspects you have hyperthyroidism, or excess production of hormones by the thyroid gland, they may recommend that you first get a blood test that measures your levels of T-3, T-4 and thyroid-stimulating hormone (TSH). High levels of T-4 and low levels of TSH are often seen in people with hyperthyroidism. If the blood test confirms hyperthyroidism, your healthcare provider may send you to ARA to get further tests.

Radioiodine I-123 scan and uptake test
For this exam, you will come to the imaging center and take a small amount of a radiopharmaceutical called radioiodine I-123, by mouth. Then you will return to the imaging center twice (once after 4 hours for a 15-minute appointment and once after 24 hours for a 45-minute appointment) to get readings and a scan of your thyroid which will enable your radiologist to make a diagnosis.

Details on getting a radioiodine scan and uptake test

Thyroid ultrasound
This exam uses sound waves to evaluate abnormalities of the thyroid gland. It is especially useful for finding nodules. Thyroid ultrasound may be used for people who are pregnant or breastfeeding, since there is no radiation involved.

Details on getting a thyroid ultrasound

If your scan indicates that you would benefit from treatment for hyperthyroidism, your radiologist and your health care provider may recommend a safe and effective treatment called radioiodine therapy, which is available at ARA.

Treatment of hyperthyroidism with radioiodine therapy

Radioiodine (radioactive iodine) therapy is a molecular radiology treatment that uses a radioactive form of iodine called iodine-131 (I-131) to destroy abnormal thyroid cells and reduce the production of thyroid hormones. It is often recommended as a first line of treatment for hyperthyroidism.

How does radioactive iodine therapy work?

Radioiodine therapy works by taking advantage of the fact that thyroid cells are very efficient at absorbing and storing iodine from your diet. When you swallow a capsule or liquid containing I-131, it travels through your bloodstream and reaches your thyroid gland. There, it is taken up by the thyroid cells and emits radiation that damages or kills them, reducing or normalizing your hormone levels.

The amount of radiation delivered by I-131 depends on the dose you receive and how much iodine your thyroid cells take up. The dose is calculated based on your body weight, age, type and extent of your thyroid issue, and other factors. Your healthcare provider will monitor your response to the treatment using blood tests and scans.

The radiation from I-131 has a very short range, so it mainly affects your thyroid gland and nearby tissues. Most of the excess I-131 that is not absorbed by your thyroid is eliminated from your body through urine within a few days.


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Treatment for hyperthyroidism is given on an outpatient basis at one of ARA’s imaging centers that performs nuclear medicine procedures.

You will go to the imaging center on the day of your procedure to receive a single capsule or liquid dose of radioiodine I-131, which you take by mouth. You will then be able to go home.

As the radioiodine moves into your bloodstream and through your thyroid gland, it concentrates in your gland and begins destroying thyroid cells.

Most people who receive radioiodine for hyperthyroidism need only one dose. You should start seeing results of decreased hyperthyroidism within a month, although it may take up to six months for the full effects to be complete.

You may have a few short-term side effects, including:

  • Feeling sore in your neck and throat for a few days
  • Nausea and vomiting
  • Sensitivity in your salivary glands. Be sure and drink plenty of water to flush them out or suck on a lemon drop or other sour hard candy to get the glands to empty.
  • Dry mouth
  • Changes in your sense of taste

You will need to have regular blood tests to monitor your thyroid hormone levels and adjust your medication if needed. You may develop hypothyroidism (low thyroid hormone levels) after radioiodine treatment, which can cause symptoms such as fatigue, weight gain, depression, and cold intolerance. If this happens, you will need to take thyroid hormone replacement medication for life.

You will need to have follow-up visits with your healthcare provider to check your thyroid function and overall health.

  • As part of your diagnosis, you will have a radioiodine I-123 scan and uptake test. See above for more information.
  • You will need to stop taking some medications that affect your thyroid function. Your healthcare provider will instruct you to stop taking anti-thyroid drugs at least three days before the procedure and stop taking thyroid hormone replacement medication five to seven days before the procedure.
  • You may need to avoid foods that are high in iodine, such as seafood, dairy products, or iodized salt, for a few days before the procedure.
  • You should not eat or drink after midnight on the day of the procedure.


  • It is a simple and effective treatment that can be done on an outpatient basis.
  • It avoids the risks of surgery, such as bleeding, infection, or damage to the vocal cords or parathyroid glands.
  • It has few side effects and does not affect other organs or tissues.


  • It may cause hypothyroidism (low thyroid hormone levels), which is easily treated with thyroid hormone replacement medication.
  • It may affect the salivary glands and cause dry mouth or taste changes.
  • It requires precautions to avoid exposing others to radiation for a few days after treatment, such as avoiding close contact with pregnant women or children.

It is important that you are not pregnant when you have this procedure as the radiation may harm the fetus. If you are breast feeding, you should stop after the procedure for the length of time recommended by your healthcare provider. You should also discuss the potential benefits and risks of other treatment options for hyperthyroidism with your healthcare provider, such as anti-thyroid drugs or surgery.

Follow directions on your patient discharge instructions to safely manage the radiation in the radiopharmaceutical as it passes out of your body in your urine. This will protect you, as well as family members and caregivers around you. If you need medical care within the first few days after your radiopharmaceutical infusion, be sure and tell your providers that you have been treated with radioiodine I-131. There may still be some radiation in your body, and your healthcare providers should take universal precautions. Most of the radiation will leave your body within 3 days.

Interacting with family and coworkers

  • Try to maintain a distance of 6 feet from others for 3 days.
  • Maintain a distance of 6 feet from infants, children, or pregnant women for 1 week.
  • Wait 3 days before returning to work, then you may return if you feel well enough.

Interacting with pets

  • Pets can be affected, too. You may want to take the same precautions with them.

Using the toilet

  • Sit while using the toilet.
  • Use toilet paper or wipes each time.
  • Flush toilet paper or wipes.
  • Flush twice with the lid closed.
  • Wash your hands each time you use the toilet.
  • Use separate towels and washcloths.


  • Sleep in a separate bed and avoid intimate contact for the first night.

Driving home from the theranostics center

  • The closest you should be to someone is 3 feet. So, if your spouse or caregiver is driving, consider sitting in the back seat.

Going out and about

  • Do not use of public transport and public facilities for 1 day.

Your healthcare provider will refer you to ARA for scans and treatment, either by giving you a paper referral or through an electronic medical system. You should receive an automated call from ARA if your referral is sent electronically. Please call (512) 453-6100 to schedule your appointment.