Radioactive iodine
Radioactive iodine (I-131) treatment: information for vets
Referral information for radioactive iodine (I-131) treatment of feline hyperthyroidism at The Narre Warren Vet.
Why choose radioactive iodine?
- Curative treatment for most cats with hyperthyroidism.
- Targets only abnormal thyroid tissue, with minimal effect on the rest of the body.
- No daily medication required after successful treatment, which can be difficult or stressful for some cats and owners.
- Avoids the long-term side effects associated with anti-thyroid medications (such as vomiting, facial itching, liver abnormalities, or blood cell changes).
Treatment outcomes
- There is a 92-95% success rate in treating hyperthyroidism with radioactive iodine.
- There is a 1-2% chance that some cats may develop hypothyroidism after treatment.
- There is a 1-2% chance that cats may not respond adequately to the radioactive iodine and require a second treatment.
Patient selection criteria
- Confirmed hyperthyroidism that is likely benign (functional adenoma/adenomatous hyperplasia). We evaluate pre and post treatment pathology results to demonstrate a well-controlled thyroid state. Cats should be on hyperthyroid medication for at least 1 month before evaluation.
- Cats with poorly controlled or difficult to control hyperthyroidism may have thyroid carcinoma and these cases tend to respond poorly to radioactive iodine treatment.
- Acceptable renal function, demonstrated by post-treatment haematology, biochemistry and urinalysis (USG).
- No uncontrolled concurrent illnesses that would significantly affect prognosis or hospitalisation/anaesthesia risk.
- Cardiac disease risk assessed if clinically indicated (e.g. heart murmur, tachyarrhythmia, gallop rhythm).
- Blood pressure assessed and hypertension managed if indicated.
- Owners understand post-treatment isolation and radiation safety requirements and can comply with home-care instructions (see below).
Radioactive iodine treatment process
- The patient is admitted to boarding the day before the procedure. They receive a physical examination with our veterinarians on the day. They are then fasted overnight ahead of the procedure.
- We use an oral form of the I-131 therapy. Cats are given a moderate sedation on the day to facilitate this.
- The patient must be isolated for 7 days. During this time, their radiation levels are high, and human contact must be restricted, hence any medical interventions or nursing care options are highly limited. For this reason, the patients should be clinically stable and have minimal co-morbidities.
- On day 7, we use a Geiger counter to measure the radiation levels. If the levels are below a certain threshold, the patients can be discharged from hospital.
- During the hospital stay, visitation is not allowed due to human health risks, but we do keep the owners updated on their cat’s progress.
Referral process and logistics
Information required
- A complete medical history including current and previous medical conditions.
- All relevant laboratory results, including pre-treatment and post-treatment pathology (CBC, biochemistry, tT4, urinalysis, blood pressure if performed and SDMA if available).
- Details of any current or previous hyperthyroid medications, including dose and duration.
- Any relevant imaging or specialist reports.
Initial contact
Cat owners can contact our clinic directly to express their interest in the radioactive iodine treatment.
Once we have received the referral information, our attending vet will:
- Review the medical information to assess case suitability.
- Arrange a telephone consultation with the owner if the patient meets the selection criteria.
- Discuss the treatment process, expected outcomes, potential risks, costs, radiation safety requirements and answer any questions.
Prior to treatment
- Anti-thyroid medication must be discontinued 14 days prior to treatment. This maximises the uptake of radioactive iodine by the abnormal thyroid tissue. Our coordinator will contact the client to remind them of this.
- We may see clinical signs of hyperthyroidism return during this period.
- Other medications should only be altered if specifically advised.
- If the patient is on any other medications, it must be easily administered with food so palatability of medications must be considered.
Stress management
A calm patient makes for a safer and less stressful treatment experience.
We recommend considering stress reduction strategies before admission, particularly for anxious cats. However, if the patient is extremely fractious, we will assess hospitalisation suitability with the client.
Our isolation wards have Feliway diffusers. However, we recommend implementing pre-visit stress management strategies where appropriate.
Post-discharge aftercare
Following discharge, owners must follow radiation safety instructions for 2 weeks.
During this period, cats should remain semi-quarantined, including:
- Keeping the cat indoors where possible.
- Avoiding prolonged or close physical contact (particularly cuddling or allowing the cat to sleep on people), less than 10 minutes of close contact per day.
- Avoiding contact with children and pregnant individuals.
- Following all instructions regarding litter tray hygiene and waste disposal.
Next steps
- We will send your practice a follow-up letter and medical history once the patient is discharged.
- The clients are instructed to book in a visit with their regular vet in 6 weeks after radioactive iodine treatment for full serum biochemistry, haematology and urinalysis.
- This is repeated 3 months later.
- Please forward results to us ([email protected]).
- If you have any questions, please contact us.
If you require any further details or would like to discuss case suitability with our vets, please do not hesitate to contact us on 9704 6463.
Narre Warren Veterinary Clinic
459 Princes Highway
Narre Warren, Vic, 3805
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Radioactive iodine
Overview
Information for cat owners
Information for vets
Enquiry form
Refer a patient
Use our enquiry form and select “Veterinarian”, or call us to discuss a case. Please send recent clinical history and blood results with the referral.
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