What You Need To Know About Radioactive Iodine Therapy



Hyperthyroidism is the most common endocrine disorder in middle aged and geriatric cats. Symptoms of hyperthyroidism can include behavioral changes, hyperactivity, weight loss, increased appetite, increased thirst and urination, vomiting, diarrhea, and rapid heart rate.

Your veterinarian may diagnose hyperthyroidism through physical examination findings and routine laboratory findings. Once a diagnosis of hyperthyroidism is made, your veterinarian will discuss options for treatment, which include medical management, surgery or radioactive iodine (I-131).

If radiation therapy is elected, Animal Imaging can provide I-131 treatment in a safe and comfortable environment for your cat. Radioactive iodine is an effective and safe treatment for hyperthyroidism. Cats treated with radioactive iodine receive a subcutaneous (under the skin) injection of the drug and are then hospitalized until the level of radiation is low enough for your cat to safely return home.

When Your Cat Returns Home
  • Small animal neurologic imaging — evaluating the brain, spinal cord and brachial plexus for abnormalities that may correlate with presenting symptoms.
  • Musculoskeletal imaging, primarily shoulders, stifles, and the pelvis
  • Vascular studies
  • Specialty studies available per Radiologist approval
  • Do not allow any pregnant women or persons under the age of 18 to come in contact with your cat. Adult exposure should be limited to 20 minutes per person, per day. Kissing and allowing your cat to lick your face should be avoided. Always wash your hands after contact with your cat or its litter.
  • Please confine your cat in your home at all times. This is the case even for cats who are primarily otherwise outdoors.
  • Your cat should be isolated to an unoccupied room and should not come into direct contact with any other household pets during this time.
  • A separate litter box, food and water bowls need to be provided for your cat. Scoop the litter each day into a plastic bag and dispose of the sealed bag in an outside trash can not accessible by children. A litter box liner may also be used. The person cleaning the litter box should wear disposable gloves.
  • If your cat happens to vomit or soil outside of the litter box, household cleaners may be used. Please be sure to wear gloves and dispose of the cleaning materials in the same manner as you would their litter.
  • At the end of the two-week period, discard of any remaining litter and clean the room. Your cat may now return to its normal routine.

A few screening tests will need to be performed prior to your cat undergoing I-131 therapy. Those tests include:

  • A chemistry profile (bloodwork) to screen for other underlying illnesses such as kidney disease. This test is performed by your referring veterinarian.
  • A urinalysis to screen for kidney disease. This test is performed by your referring veterinarian.
  • A thyroid scan to evaluate the thyroid itself and check for benign or malignant thyroid disease. The thyroid scan can be performed at Animal Imaging on an outpatient basis.

Once the screening tests are performed and your cat is determined to be a good candidate for I-131 therapy, arrangements can be made at Animal Imaging to administer the therapy. Patients are admitted to Animal Imaging on a Monday and return home on Friday.


Can I bring any toys, bedding, food, etc. for my cat?

We recommend that you bring your cat’s regular diet so that we can maintain him/her on what you normally feed at home, although we can provide food if necessary. Toys and bedding are permitted, but due to the radiation levels in the I-131 therapy area, those items will be discarded at the end of your cat’s stay.

Will my cat experience any side effects from the drug?

Very rarely (approximately 2% of treated cats) cats may become hypothyroid after the administration of I-131. In such cases, these cats can return to normal with supplementation of thyroid medication. Some cats may experience a few weeks of lethargy after returning home. These side effects are rare and the benefits of treatment far outweigh the risks of no treatment at all.

Can I visit my cat during his stay?

Unfortunately, we cannot allow visits during your cat’s stay due to the radiation levels. We do, however, encourage you to call and check on your cat’s status as often as you like.

What follow-up care do I need to provide for my cat after therapy?

Your cat’s thyroid levels should be rechecked in approximately 2 months after treatment to ensure that the thyroid has returned to normal. This test can be performed at your regular veterinarian’s office.