Radioactive Iodine Treatment for Hyperthyroid Cats

Radioactive Iodine Therapy (I131) for Hyperthyroid Cats

Referring Veterinarian Information 


Sage Redwood City is NOW offering radioactive iodine treatment for hyperthyroid cats.  As you know, radioactive iodine (I131) is the treatment of choice for cats with hyperthyroidism.  Many of these cases are straightforward but others have concurrent illness that makes them a bit more complicated. For our program, we request that you have your client schedule a consultation with an internal medicine specialist at SAGE to discuss the treatment. This consultation will include discussion of the pros and cons of radioactive iodine as well as making sure they understand the restrictions when the patients are discharged post treatment and any other issues that we feel need to be followed up. For most patients, follow-up after treatment will be performed through you as the primary vet rather than needing to come back to SAGE.


Cost of I131 treatment is $1725 which includes the treatment and hospitalization from Tuesday to Friday. The consult appointment and any additional diagnostics are not included in this fee.

    • All cats must have a consultation with a SAGE internist (at any location) to determine if I131 is appropriate and to rule out any other concurrent diseases
    • All cats must have 3 view chest xrays either from pdvm or SAGE within 30 days of treatment
    • All cats must have total T4 greater than normal (free T4s are often elevated with concurrent disease)
    • All cats must have a cbc, chemistry panel and urinalysis within 1 month of I131 treatment
    • The patients T4 level off methimazole is used to determine I131 dose. Ideally, either use pretreatment T4 or stop methimazole for 1 week and recheck just prior to treatment date
    • A methimazole trial should be conducted to determine effects of lowering T4 on kidney function. A  methimazole trial consists of normalizing  the T4 and then evaluating the patient’s BUN/creatinine. If the patient cannot tolerate methimazole, then I131 can be pursued without this step after the client is warned of unmasking chronic kidney disease in the patient.
    • Cats should be off methimazole for 1 week prior to treatment date

Post treatment follow-up unless directed otherwise by Internist:

    • One month post treatment- check renal values and T4
    • Three months post treatment: check renal values and T4

If you have questions or prefer for us to call client to schedule the appointment, please email us at

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