Prior to being admitted through Hypurrthyroid Treatment for Cats for radioiodine treatment, all patients are required to have had diagnostic testing completed within the previous 30 days.  These diagnostics include:

  • CBC (complete blood count)
  • Blood chemistries (to check kidneys, liver, blood glucose, electrolytes, etc.)
  • Thyroid hormone (T4) level
  • Urinalysis
  • Chest radiographs
  • Blood pressure
  • Abdominal radiographs and/or abdominal or cardiac ultrasound may be appropriate in some cases (if there is suspicion of other concurrent nonthyroid illness, such as heart, intestinal or other issues that we should be aware of prior to I 131 treatment)

We want to be sure that your cat is healthy enough to stay with us for the duration of the radioiodine treatment period.

If your cat has previously been treated with medication (Felimazole, methimazole, carbimazole, PTU) for hyperthyroidism, these should be discontinued for at least 7-14 days prior to treatment with radioiodine. If your cat has been on Hill’s Y/D diet for treatment of its hyperthyroidism, it recommended that your cat be off the diet for 6-8 weeks prior to treatment with I 131.


The morning of your cat’s scheduled treatment, you will have an appointment scheduled for your cat to be examined by Dr. Currigan.  The doctor will then provide a presentation about the radioiodine procedure, including both your responsibilities regarding after care and ours while your cat is hospitalized.  Many owners find that they have additional questions during this presentation, and we are happy to answer any and all questions.  Your confidence in our care for your cat is essential.

We ask cat owners to bring enough food for the duration of the hospitalization period, especially if your cat is on a less common or unique diet that we may not carry.  Many cats are more inclined to eat well while away from home if the diet is familiar.   Although we are unable to accommodate larger toys, bedding, blankets, etc. from home as our safety guidelines and space will not always allow these items to return home with you, we do encourage owners to bring a small toy and/or piece of clothing (such as an old T-shirt) that we can keep in your cat's housing area to help reduce any anxiety. (Note that due to safety guidelines, we may not be able to send these items home with you, however).

No fasting is necessary prior to radioiodine treatment, so go ahead and feed your cat on the day of admission.   All, or at least the majority, of the tests that we want completed prior to admission day should have already been done.  However, if further tests are required, they can be performed by us, but in some cases, that may necessitate our having to postpone the treatment to another day.


Once admitted to our facility, your cat will receive a mild anti-emetic (anti-vomiting) medication that also helps to relax him or her. We want to be sure that the cat does not vomit the radioiodine once given. We are also not hesitant to administer additional anti-anxiety medication – at any time throughout the treatment period – if we feel it would make your cat more comfortable. (Most patients ‘opt in’, not surprisingly, to receiving help in reducing their anxiety!).

The radioiodine is given as a single oral dose of radioiodine on the day that your cat is admitted.  After the treatment is administered, your kitty is placed in a special, lead-lined radiation isolation ward (as required by law), away from other animals not receiving this treatment. During the hospitalization stay, which is usually 2-5 days, your cat’s radiation levels and other vital signs are monitored closely.

We will send pictures and updates to patient owners by email or text daily. Owners are always welcome to call Cat Hospital of Chicago as well for updates. We understand how much you miss having your furry friend by your side!

Although it is unlikely that radioiodine patients will become ill during their hospitalization with us, we know that most hyperthyroid patients are senior and geriatric cats, and not uncommonly, they have other health issues in addition to their thyroid disease. Any patient that becomes ill, even critically, while hospitalized for radioiodine treatment, will receive full care with arrangements made to minimize radiation exposure to our personnel. Rest assured that needed treatment will not be denied.


Once your cat’s radiation levels have declined below the maximum allowed by federal and state law prior to being released from the hospital (usually 1-5 days), your cat is able to return home.  However, your cat will still have a low amount of radiation in his or her body.  You may be surprised to know that this amount of radiation is far less than what you would have if you were treated with radioiodine, and is very similar to the amount of radiation that you might receive if you flew across the country in an airplane!    Nonetheless, because there is still some radiation in your cat’s body (and most cats do not use toilets, at least not 100% of the time!), there are legal requirements for owners once the cats are at home, so we want you to exercise caution during the first week or two at home.

What precautions are important?

At the time of I 131 treatment, guidelines will be provided and reviewed with you to minimize unnecessary radiation exposure to family members for the first 2 weeks following the cat's discharge from the nuclear ward at our hospital. Briefly, precautions that we recommend include:

  • Your cat should be discharged from our care in a non-cardboard carrier.
    If a cardboard carrier is used, and your cat should urinate (or defecate or vomit) in the carrier, necessitating disposing of the carrier, you will need to wait 81 days prior to putting the carrier in the trash until the level of radiation in the urine (or excrement) has reached a low enough level for routine dumping in the trash. (As noted in the bullet point below, garbage dumps have radiation detectors that will detect radiation and you will incur a hefty fine if it is found!). Hard-sided carriers that can be wiped clean are recommended over cardboard carriers. (If toilet paper is use to wipe the carrier clean, it can be flushed into the toilet; if paper towels are used, they will need to be stored for 81 days prior to disposal; if a rag is used, it can be rinsed and then laundered as usual – but no bleach).
  • Keep your cat indoors (or, if outside, the cat should be under your direct supervision and on a leash in order to minimize the possibility of radiation exposure to other people) for 14 days after release from our hospital.
  • Do not allow children under the age of 18 or pregnant women to have any contact with your cat, food dishes, toys or litter box(es) for 14 days after release. If you are unable to prevent contact between your cat and children, or you are pregnant and have no way to prevent your cat from sleeping in your bed with you at night, we recommend that your cat be boarded during this 2-week period.
  • Limit close up contact time (cuddling, lap time) with your cat to no more than 20-30 minutes per person per day (all at once or spread throughout the day). Avoid sleeping with the cat. You can pet your cat at arm’s length distance as much as you want during this 2-week period as this is a safe distance. (It is not necessary to wear gloves to pet your kitty unless there is a chance that your cat has accidentally soiled its coat with urine or feces). This is recommended in order to minimize your lifetime cumulative exposure. Exposure to other pets is fine.
  • Wash hands carefully with soap and water after handling your cat, its food dishes and litter box(es).
  • Wear disposable gloves (we will provide to you at release) when handling litter box excrement. Scoop the litter twice daily for 14 days after release. Use a plastic liner in the litter box for this 2 week period. We recommend use of flushable scoopable litter. All soiled litter must be collected and either flushed down the toilet (ONLY if using flushable litter!) or stored for 81 days after release (if non flushable litter is used).
    Remember that pregnant women and children under the age of 18 should not have any contact with your cat’s waste products for at least 2 weeks after release from Hypurrthryoid Treatment for Cats. Place gloves and any other items that have been in contact with your cat’s urine or feces in a double lined garbage bag and after the 2-week period, place the bag in a garage, high rise porch or other area of the home away from children and other animals for disposal in 81 days (along with any non scoopable litter).
  • To store the litter (if not using flushable litter): Purchase a large bucket (we use 5 gallon paint buckets in our nuclear ward) and line it with a non-scented trash liner. Scoop all urine and feces twice daily (from the I 131-treated cat, as well as any other cats that may be using the same litter box as the treated cat). At the end of the two-week period, dump the entire contents of the litter box into the bucket (including the litter box liner), along with any gloves or other items that have been in contact with your cat’s urine or feces during this two-week period. Put the lid on the bucket, assuring that it is well secured, and then store it in a place, preferably out of doors, that is safe from wildlife, etc. (such as the garage or high rise porch; if kept inside, it should be kept away from food or high traffic areas and instead stored in a basement storage area, utility room, etc.). Do not dispose of the bucket of litter prior to 81 days (after the 2 week period of collection) since garbage dumps have radiation detectors that will go off if radiation is detected and you will be charged a significant fine!
  • There is no risk for other pets. Your cat can share the litter box with other cats in your home, and can play and sleep with other pets as usual.


The cost for any treatment for feline hyperthyroidism is significant. The fee for radioiodine therapy ranges from $1,685 - $1,910, depending on how much drug is required to treat each patient (which also factors into the required length of hospitalization in the nuclear ward). This fee includes the radioiodine itself, the cost of hospitalization and monitoring, blood pressure measurements as needed throughout your cat’s stay, and any oral anti-anxiety medications or appetite stimulants required while hospitalized. Any additional treatments required during the hospitalization stay would result in additional fees. Boarding beyond the initial hospitalization period would also result in additional fees. While this is a higher upfront cost than other options, it is less expensive than other options over the lifetime of the cat. Radioiodine treatment generally results in fewer thyroid blood tests for the remainder of the cat’s life as well, which makes the treatment more cat-friendly from the patient’s point of view as well.

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Please note:  Because we must order the dose of radioiodine before the treatment is administered, and the dosage is tailored specifically for your cat, cancellation of a scheduled appointment less than 72 hours before the appointment time will result in a charge of $335.