Radioiodine Outpatient Information


The thyroid glands are located in the neck of the cat are responsible for producing thyroid hormone. An excess of thyroid hormone production causes hyperthyroidism. The thyroid glands trap Iodine from the blood stream and concentrate it within the gland. When a cat is given radioactive iodine-131 the dose is concentrated in the thyroid gland. The radiation then destroys the overactive thyroid gland but doesn’t cause damage to other parts of the body.

Cats receive a single dose of radioactive iodine by either subcutaneous injection or by a capsule given by mouth. This single treatment will cure 95-98% of cats. It will take about a month for thyroid levels to return to normal in most cats. A small number of cats will remain hyperthyroid after treatment, if this is the case your cat will need to have either a second treatment or to use other medical or surgical methods of treatment. A small number of cats will have very low levels of thyroid function after treatment (hypothyroidism) that may require lifelong supplementation with thyroid hormone.

Side effects from radioactive iodine therapy are very rare, 1.5% cats will have temporary difficulty in swallowing or a change in voice.

Compared to people cats receive quite a low dose of radioactive iodine-131 for the treatment of hyperthyroidism. This is because they are much smaller than people and have smaller thyroid glands. Even though your cat will be radioactive when it goes home, following our guide will ensure that any radiation exposure at home is well within the safe levels determined by the government.

The risk of radiation exposure comes both from your cat directly and also from any bodily fluids or wastes such as urine, saliva, faeces and vomit.

To help protect yourself and other in the house from radiation exposure you should follow some simple rules for the first 3 weeks

  • Limit the time spent with your cat
  • Maximise the distance between yourself and your cat – radiation levels drop very quickly as distance increases (by the inverse square law)

Children and unborn babies are more sensitive to radiation so children and pregnant women should not be responsible for caring for a treated cat for at least 21 days after treatment.

WHAT DO I HAVE TO DO AT HOME? For first 7 days

  • Your cat must be housed in a room by itself for the first 7 days after treatment. This room must not be entered other than for brief periods to care for your cat. This room must be at least 2 metres from any area of the house that is frequently used, i.e. bedrooms, lounge room, kitchen. Think about any rooms that may be above or below the location in which the cat is housed.
  • Your cat must use a litter tray with clumping flushable litter for the first 7 days.
  • You must use disposable gloves when handling the litter tray. The litter tray must be carried to the toilet and the clumps of urine and faeces must be removed from the litter tray using a scoop and flushed down the toilet. This needs to be done twice daily for the first 7 days. The disposable gloves should be removed, placed in a plastic bag and discarded into the rubbish.
  • The maximum amount of time that any individual person is to spend in close contact with the cat is 15 minutes per day. This time must include feeding, changing water and cleaning the litter tray. During this time you may stroke your cat but you may not pick it up or allow it to sit on you.
  • Wash your hands after contact with your cat.

For Days 8-21 After Treatment

  • Your cat is allowed inside and outside and does not need to be continuously confined.
  • Your cat must not sleep in the same room as you for this period. Your cat should be a minimum of 1 metre from a bed, remember that radiation can travel through walls.
  • You must limit close contact with your cat to 30 minutes per day for each person.
  • The cats litter tray should be cleaned once daily using a scoop and wearing disposable gloves. Litter and gloves may be discarded with the household waste.
  • Wash your hands after contact with your cat.

From 22 days after treatment you may treat your cat as normal as the levels of radiation will have fallen to very low levels.


  • My cat escapes in the first 7 days

Catch your cat and place it back in its room as soon as possible. Hold your cat at arms length if possible while moving it back to its room.

  • My circumstances have changed and I cant follow the guidelines any more

Contact the Radiation Safety Officer at Creek Road Cat Clinic and we will develop a suitable plan. It may be necessary to admit your cat to hospital.

  • My cat is unwell and needs to see a vet within 21 days of treatment

If possible see a vet at the Creek Road Cat Clinic, the clinic has a 24 hour emergency service. If this is not possible advise your vet that your cat has been treated with radioactive iodine-131, the dose and the date the treatment was given. Advise your vet to contact the Radiation Safety Officer at Creek Road Cat Clinic if they require advice on the safe handling of your cat.

  • My cat urinates, defecates or vomits outside its litter tray

Use disposable gloves and paper towels to clean up the mess. Be very careful not to step in the mess. Flush any paper towels down the toilet and place the disposable gloves in a bag and place in the outside rubbish bin. Wash your hands thoroughly with soap and running warm water for at least 5 minutes. Contact the Radiation Safety Officer at Creek Road Cat Clinic.

  • My cat scratches or bites me

Clean the wound under running water for at least 5 minutes. If the wound is bad seek medical attention and advise the medical staff that you have been bitten or scratched by a cat that has had radioactive iodine-131 treatment. While there will be some radioactivity transferred in saliva from a bite it will be a very small amount. Please contact the Radiation Safety Officer at Creek Road Cat Clinic

  • I spill urine, faeces or vomit on my skin or clothes

You should remove any items of clothing that are contaminated and place them in a plastic bag. Wash any areas of skin that have been contaminated with soap under running warm water for at least 5 minutes. Clothes should be washed promptly. Contact the Radiation Safety Officer at Creek Road Cat Clinic for further instructions.


  • Please arrange an appointment with your regular vet for a physical examination, weight check and blood test for thyroid and kidney function 4-6 weeks after treatment.

Please do not hesitate to call the clinic if you have any questions or concerns.