I-131 Information for Veterinarians

I-131 Information Pack for Referring Download PDF Vets August 2021


At North Nowra Veterinary Hospital we are pleased to offer Iodine-131 (radiation) for the treatment of feline hyperthyroidism. Radio-iodine is the treatment of choice for hyperthyroid cats and has numerous benefits over ongoing medical management. This includes better and more stable clinical outcomes, and a cure rate exceeding 95% of cases treated.

At North Nowra we have been offering this treatment to cats and their owners from the Illawarra, Shoalhaven, South Coast and Southern Highlands since 2009. In that time, we have treated around 300 cases. We continue to accept cases for treatment, and in doing so we undertake to treat your clients and their cats as we would our own, and to an excellent standard.

The purpose of this page is to make the process of sending cases simpler and easier, by providing a list of the bits of “data” we need to assess a case and determine the appropriate dose of I-131.


To accept and plan the treatment of a confirmed hyperthyroid case we require:


  • Total T4 (at time of initial diagnosis)
  • Urea level (ideally normal, please include reference range)
  • Creatinine level (ideally normal, please include reference range)
  • USG (cats with a USG of > 1.035 are typically good candidates for I-131)
  • Assessment of size of thyroid glands (goitre) by palpation (cm or mm but please make this clear)
  • Assessment of severity of clinical signs (mild, mild-moderate, moderate, moderate-severe, severe). This is a subjective judgement taking into account factors like degree of weight loss, appetite, vomiting/diarrhoea, heart rate/presence of murmur, changes in behaviour/hair coat.


If a patient has been treated with carbimazole or methimazole for any period, we need to ensure a break for 14 days prior to administration of I-131. We will ensure this is arranged when liaising with your client. Thank you for entrusting us with the care of your patients. If you have any questions, please contact us.


Kind Regards, The North Nowra Veterinary Hospital Team