Radioiodine questions and answers for owners


Radioiodine treatment for cats with hyperthyroidism is now being offered at ChesterGates Veterinary Specialists. Below are frequently asked questions and answers for owners.

What is hyperthyroidism?

This is an over-active thyroid, when a cat’s thyroid glands are producing too much thyroid hormone. It causes weight loss despite an increased appetite, increased thirst, sometimes vomiting and diarrhoea, and increased activity levels. A blood test can identify the condition. If left untreated, hyperthyroidism can adversely affect the heart and the kidneys and can cause high blood pressure.

What treatments are available for hyperthyroidism?

  • Tablets or a prescription diet can control the effects of the overactive thyroid by preventing thyroid hormone production. These treatments require regular ongoing monitoring via blood tests, for the cat’s lifetime. Some cats also experience side effects which means that they cannot take tablets.
  • Surgery or radioactive iodine (RI) treatment offer a cure of the condition, which means that there is usually less requirement for long term monitoring. Surgery does carry risks of complications, particularly inadvertent loss of parathyroid gland tissue which maintains blood calcium levels. Unlike surgery, RI treatment does not require a general anaesthetic, it will not run the risk of causing low calcium, and it is unusual that repeat treatment is required, whereas often the two thyroid glands are removed one at a time when surgery is undertaken.

What happens if I would like my cat to have RI treatment?

Your cat would need to be referred by your local vet. We would meet you and your cat at an appointment at ChesterGates to assess if RI treatment would be the best choice of treatment, and to give you the opportunity to ask any questions you have. The assessment ideally takes place while your cat is taking tablets (or on a prescription diet) to control hyperthyroidism. The assessment always involves:-
  • Take a full medical history of and examination of your cat,
  • Blood pressure- measurement,
  • Blood and urine tests particularly to check kidney function and thyroid hormone levels.

We do tailor assessment to the individual, so sometimes we also recommend additional tests such as ECG, or ultrasound of the abdomen or heart, depending on particular factors in your cat’s history and examination.

Most cats are a good candidate for RI treatment. An appointment would be made for treatment following assessment. Anti-thyroid medication or the prescription diet must be stopped two weeks before RI begins.

Are there any side effects of radioiodine treatment?

Around 95% of cats are cured after a single injection and no further treatment is required. Therefore occasional treatment failures (5%) are inevitable; most of these patients show a partial response and then respond fully if a second treatment is given. Occasionally, the treatment works too well and an underactive thyroid is the result. This does not always require therapy, as any normal thyroid tissue will be unaffected by the injection and it can recover function over time. However, some patients will require thyroid hormone supplementation, if they show signs of an underactive thyroid or if they have kidney problems alongside the underactive thyroid.

What does the treatment involve?

The treatment involves a single injection of radioactive iodine given under the skin at the back of the neck, which usually requires a light sedation.

How long does the hospitalisation usually last for?

Your cat will stay with us for two weeks following the RI injection, in order for the radioactivity administered to diminish to safe levels for in-contact human beings.

Can I visit my cat during the hospitalisation?

Unfortunately not, it is not possible for owners to enter the radio-iodine ward for health and safety reasons. However we are able to provide you with updates on a regular basis.

Can I leave something from home with my cat during the hospitalisation?

You are welcome to leave a familiar item with your cat whilst hospitalised. At the end of the hospitalisation we will have to dispose of these items because of the radioactive contamination. We will therefore ask you to bring something small as the quantity of radioactive waste we can produce is very controlled.

How will I know when my cat is ready to come home?

Your cat’s radioactivity will be assessed before discharge and once it reaches a safe level, you will be contacted. An appointment will then be made for your cat to go home.

What do I have to do when I take my cat home?

When your cat is discharged you must follow some guidelines as there will be some low-level radioactivity still present for at least 2-3 weeks following discharge. These guidelines will include:
  • Minimal handling of your cat and wash your hands straight afterwards,
  • Wear gloves and double bag any waste from your cat before disposing in general rubbish,
  • Avoid your cat being in contact with children and pregnant ladies.

Do I need a check-up appointment once my cat has gone home?

Yes our specialist medicine team will organise to see your cat approximately one month after discharge, blood and urine tests are taken at this point.

If you have any further questions regarding treatment, please do not hesitate to contact us.

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