131-I Therapy

Please note, due to an increased demand for I-131 therapy, the Veterinary Medical Center has postponed scheduling any new therapy patients until May 31, 2023. 

Download new client information - Radioactive Iodine Therapy.pdf


Radioactive iodine (I-131) therapy is an accepted treatment for cats with hyperthyroidism. Numerous publications advocate the use of I-131 therapy for cats with thyroid adenoma or carcinoma. The therapy is noninvasive (compared to surgery) and usually only 1 dose is enough to return the animal to a normal, euthyroid state (compared to daily administration of conventional anti-thyroidal medication). Cats typically return to a normal, euthryoid state 2-4 months after I-131 treatment.

Scheduling I-131 therapy and pretreatment evaluation

Due to limited available space and personnel, and to limit human exposure, the number of animals scheduled for I-131 therapy at the OSU Veterinary Medical Center is limited. For appointments, call the OSU Veterinary Medical Center: (614) 292-3551.  Please fill out the referral form to provide pertinent medical history and labwork needed for assessment of the patient.

At the OSU Veterinary Medical Center, the minimum pre-treatment evaluation for each cat consists of:

  • CBC, Chemical profile, Urinalysis, Blood Pressure
  • Serum T4 concentration

Further evaluation is available, if necessary, and may consist of:

  • 99m Tc-pertechnetate scintigraphy (thyroid scan)
  • Nuclear medicine renal function studies: GFR and ERPF (if needed)
  • Thoracic radiographs and echocardiogram (if needed)

Patient's care during treatment

After I-131 administration, the cat is housed in an isolation ward to comply with State of Ohio, radiation safety regulations. During isolation, no owner visits are allowed, and only trained radiology personnel can handle the cat to provide care. Each cat’s radiation level is monitored daily. Cats are released to their owners when their radiation exposure level is below 50 mR/hr at the skin surface over the thyroid glands (usually 3 – 7 days after I-131 administration).

Learn about patient care after release