Referring Veterinarian Information and Work-up Instructions

Iodine 131 is the standard of care for cats with hyperthyroidism. I131 has shown to dramatically increase the life expectancy of cats with hyperthyroidism, with the average life expectancy for cats treated with I131 is 4 years.

I131 is over 95% effective. Most of the patients who do not respond to a first treatment with I131 can be successfully treated for a second time. There can be biological variation among cats that require some cats to need a larger dose than the typical prescribed dose. If a second dose is needed, it will be done at a significantly discounted price.

I131 is best suited as a first line therapy for stable patients, with or without concurrent other stable medical conditions. If you are unsure if your patient is a good candidate, please call to discuss the case with us.

When the cat arrives at our facility, we will perform an exam, administer the I131, and monitor the patient several times a day. We will administer other medications as prescribed for the patient.

Diagnostic Testing Required:

  1. CBC, biochemical profile (preferably with SDMA), T4, and urinalysis. These values should be within 90 days of admission.
  2. If your patient has been on methimazole for more than 90 days, please discontinue the methimazole for at least seven days and perform a new T4 level. We must have these results no later than 6 days prior to the treatment date. The I131 dose is calculated on these results. Your client’s appointment will need to be rescheduled if these results are not received in time. Treatments always occur on Mondays – we need testing results to us by 5:00 pm the Tuesday before scheduled treatment.
  3. Lateral and DV (or VD) thoracic radiograph. You can send by e-mail to:
  4. If the cat has been on methimazole prior to radioiodine administration, we require the cat to have been off the medication for at least 7-14 days prior to I131 treatment to ensure adequate update of the injection.
  5. If the cat has been treated with y/d, that diet needs to be discontinued for at least 2 weeks prior to I131 injection.

Patient Admission Information:

  1. Patients are admitted for therapy by appointment only, and treatments are performed on Mondays.
  2. Patients are hospitalized for approximately 3-4 days. Clients cannot visit patients during therapy nor can patients be removed/discharged until officially released.
  3. Clients cannot terminate therapy early or arrange for early releases once therapy has begun. These are State and Federal regulations.
  4. Clients can ‘virtually’ see their pets via individual cameras for each cat.
  5. We will send a daily text or email to update owners on their cats.
  6. In the unlikely case where the patient dies during their stay, we are required to hold the remains for approximately 90 days.

Dismissal Policy

Patients will be excreting a small amount of radiation upon dismissal. The clients are given strict dismissal instructions on handling pets for 2 weeks post-dismissal. If clients are unwilling or unable to follow these precautions, they should consider surgical or medical management.

Uncommonly Seen Side Effects

  • Hypothyroidism. A very small percentage of treated patients will have lifelong hypothyroidism. Most cases of hypothyroidism are transient and resolve within 4 months post-treatment. We do everything possible to use specific I131 dosing to greatly minimize the chance of creating hypothyroidism.
  • Radioactive iodine treatment DOES NOT cause kidney disease. Chronic kidney disease and hyperthyroidism are both very common problems in senior cats. Because hyperthyroidism can contribute to worsening of kidney disease and heart disease, it is preferable in most cases to correct the hyperthyroid condition, and eliminate that as a comorbidity. If you are unsure if I131 is the best option for your patient, please contact us to talk about the case.