A single dose of radioactive iodine (I131) is given by subcutaneous injection. The iodine is concentrated in the thyroid gland where it emits beta-radiation, killing the surrounding hyperfunctioning cells. The parathyroid gland function is unaffected. The iodine that is not concentrated in the thyroid gland is very rapidly eliminated in the urine, saliva and sweat in the first couple of days following the injection.
The remainder is very slowly eliminated due to thyroid hormone turnover (with the I131 incorporated into the hormone) and due to decay of the isotope (the half-life of I131 is eight days). Cats must stay with us in an isolation facility until most of the radioactivity has been eliminated. A Veterinary Nurse feeds them and cleans their cages daily.
What does it cost?
The current cost of treatment for 2023 is £3,195 which includes blood and urine sampling prior to treatment, echocardiography, the iodine itself and hospitalisation for up to two weeks. In the rare situation that additional hospitalisation is needed, this will be charged per day. If necessary, fees for other treatments or investigations will be discussed with the client and charged accordingly.
We require a £500 deposit at time of booking. This is non-refundable unless a cancellation is made at least two weeks prior to the appointment or we determine the cat is not suitable for treatment. If a client is insured, this deposit will be paid back upon receipt of payment from the insurance company.
How successful is it?
A single radioactive iodine injection is successful in >95% of cats. There are a small subset of patients that require a second injection of iodine therapy. Please note that we cannot treat thyroid carcinomas at this time.
How quickly will you know if it has worked?
The thyroid hormone concentration is generally normal or low by the time cats are discharged from the service. Occasionally, it takes a few weeks before the patient reaches euthyroid status. We ask for monitoring once the patient has been discharged at 3-6 months post treatment.
What needs to be done before the appointment?
Cats need to be confirmed as hyperthyroid, on a total thyroxine (TT4) concentration above the laboratory reference range at an external laboratory.
Where possible, to allow evaluation of renal function and to minimise any clinical deterioration, we recommend that cats are treated with medical therapy prior to RI treatment. Renal function will need to be monitored as the patient reaches euthyroid status in case underlying chronic kidney disease is ‘unmasked’. This occurs because the glomerular filtration rate (GFR) is increased in the hyperthyroid state and the cat’s true renal function can only be evaluated once GFR reduces with normalisation of thyroid hormone. If the patient reaches euthyroid status and is not azotaemic, the cat is an ideal candidate for treatment. If the patient is azotaemic after normalisation of thyroid hormone, please contact us to discuss the case, as some cats are still suitable for treatment.
We request that bloods to assess renal function and thyroid levels are performed within 4 weeks prior to referral, to ensure the patient remains clinically stable.
The owners must be instructed to stop medical therapy two weeks before their appointment with us.
How long must the cat remain in isolation?
All cats treated with radioactive iodine will stay in the unit for a minimum of 8 days following the injection. Discharge from the service is based upon the cat’s levels of radioactivity. If a cat is discharged at 8 days, the owner will sign a document agreeing that strict conditions will be in place until 14 days post-injection.
A further set of precautions will be applicable until 28 days have elapsed since injection. If the early discharge criteria cannot be agreed patients will remain in the isolation unit until the full 14 days have elapsed.
If the patient needs to stay beyond 14 days (e.g. the owner cannot adhere to precautions at home), then additional hospitalisation charges will occur.
Which cats aren’t suitable for treatment?
Although thyroid carcinoma can be treated with radioactive iodine we cannot currently offer this at The Veterinary Surgery.
As we are restricted in our handling of patients once they can be injected with iodine cats that require handling for daily medications (such as insulin injections) are not suitable. However, we may be able to take patients that are managed by oral medications given in food,
Cats with concurrent health conditions that may deteriorate whilst in our care. We cannot attend to a cat once it has been injected if it were to fall ill, due to the high risk to human health. This is why we need to extensively screen our patients to ensure that the treatment is right for them.
There is no ability to reduce the required isolation time within the unit; we are also unable to accommodate owner visits due to the strict health and safety requirements. If an owner is not comfortable with this, then RI treatment is unfortunately not a viable treatment option.
What is needed after injection?
We recommend that cats should have a check-up at three and six months after their injection date. At these checks we recommend a minimum of:
- Blood pressure check
- Total T4 and biochemistry sample
- Bodyweight measurement
- General physical examination
In addition to this, we recommend urinalysis (dipstick, microscopy, USG and urine protein:creatinine ratio) for any azotemic cats. Please forward any results to us so that we can keep them with the patient’s files. Please feel free to call us for any advice you require.
For more information please download our leaflet for vets here: Radioactive Iodine Therapy Referral Leaflet