College of Veterinary Medicine

Veterinary Teaching Hospital

Radioactive Iodine Treatment of Hyperthyroid Cats

Face of Siamese Cross Cat

I-131 Treatment for Hyperthyroidism in Cats

  • Approximate cost (total bill which includes examination fee, I-131, some limited diagnostic evaluation if needed, and hospitalization): $950-$1200; a cardiology evaluation if needed could add $300 to this estimate.
  • Length of time in hospital: 6 to 8 days. The campus Radiation Safety Office, not the clinician, authorizes release of the cats)
  • Route of I-131 administration: single subcutaneous injection
  • Side effects: none expected, though, as with other treatments for hyperthyroidism, decreases in renal function (please see below) may be observed following I-131 therapy; hypothyroidism is uncommonly observed.
  • Tapazole®: We would like to have Tapazole® discontinued 2 weeks prior to treatment with I-131.


Current lab tests including a minimum of BUN, Creatinine, urine specific gravity and TT4 during a euthyroid state (or nearly normal T4 ) induced by methimazole treatment, should be available in an otherwise healthy cat. If a cat is showing signs of illness a CBC, Chemistry panel, UA, and possible further diagnostics may be required prior to injection. Bloodwork can be sent with the client, or drawn at WSU. Bloodwork may be repeated at WSU at the discretion of the admitting/supervising clinician.

We often ask for Faxes (509-335-3330) of recent laboratory results- especially the CBC, chemistries and urinalysis- so that any concerns we have may be addressed prior to the trip to Pullman.

Hyperthyroidism and chronic renal failure

Cats with both hyperthyroidism and chronic renal failure may have an increase in kidney waste products (azotemia) after treatment for hyperthyroidism.

For the recently diagnosed hyperthyroid cat, the option of trial therapy with Tapazole® should be considered so that the effect of treatment on renal function can be evaluated. It is generally felt that if serum BUN and creatinine concentrations remain unchanged with normalization of T4 after Tapazole® treatment, then definitive therapy with surgery or I-131 is unlikely to be associated with worsening of renal function post-treatment. Development of azotemia following implementation of Tapazole® treatment is not a contraindication to I-131 treatment, but does create management concerns that may impact the decision to treat with I-131.

Discharge from the hospital

Length of time in hospital: 6-8 days average (shortest has been 5 days, longest 14 days; the campus Radiation Safety Office, not the clinician, authorizes release of the cats). Discharge instructions will include guidelines on special handling of urine and feces, and maintaining the cat at a safe distance from small children, or pregnant women for two weeks post release.For further information or to arrange referral, please contact the Referral Medicine Technician, Roland Munson at 509-335-0711.

Last Edited: Apr 07, 2014 12:30 PM   

Veterinary Teaching Hospital PO Box 647060 , Washington State University, Pullman WA 99164-7060, 509-335-0711, Contact Us Safety Links