Advanced Care

Feline Radioactive Thyroid I-131 Treatment

What is hyperthyroidism?

Hyperthyroidism is a condition resulting from secretion of excess thyroid hormone from the thyroid glands. In cats, this most often results from adenomatous hyperplasia (overgrowth) or adenoma (benign tumor) of the thyroid gland. Thyroid cancer (carcinoma) is a rare cause of hyperthyroidism in the cat.

How do we treat hyperthyroidism in cats?

At VCA Cat Hospital of Chicago, in addition to other treatment options for this disease, we offer radioiodine (I-131) therapy, which is a well-established effective, one-time treatment for hyperthyroidism. Radioiodine treatment is offered only at facilities with specialized nuclear medicine licenses. We are the first such treatment center within the Chicago city limits.

Cats are administered a single radioactive capsule by mouth, its dosage tailored for each patient, followed by a brief stay with us. That’s it—and your best friend and beloved family member’s thyroid condition is permanently cured. That’s right—for the large majority of patients, no medication or treatment is needed after radioiodine treatment. This is one of the best gifts you can give to your feline companion—no oral medications!

About Our Team & Treatment Center

Dr. Currigan with Gracie the cat at VCA Cat Hospital of ChicagoWe provide state-of-the-art treatment for our patients in a warm, comfortable environment that has the emotional and physical well-being of every single patient at the forefront. We love cats, and we are especially fond of senior and geriatric cats, the cats most susceptible to developing hyperthyroidism. We know that cats prefer not to be away from home—our own included. We are your hyperthyroid cat’s best friend and it shows in every bit of detail and personalization taken into consideration for each patient under our care for treatment in our facility. Our hyperthyroid patients are housed in spacious, quiet cages, with soft bedding, hiding cubbies, perching benches, and, within Federal and State nuclear safety limits, receive all the attention that they want (or don’t want)—we respect their preference.

Dr. Colleen Currigan and her colleagues at VCA Cat Hospital of Chicago, Drs. Daphne Thompson, Elizabeth Czerwonky and Mariah Foose, all take part in the care and treatment of our patients receiving radioiodine treatment. Our team members all excel in gentle cat-friendly patient handling and care and they work hard to support our veterinarians to assure all hyperthyroid cats receive individualized care.

Our treatment center is closely regulated by the Illinois Emergency Management Agency and the Federal Nuclear Regulatory Commission.

Our Radiation Safety Officer and Radiation Physicist make quarterly visits to our treatment center to assure that we are current with all radiation safety measures—for our patients, our "human team", and our patient’s owners.

Additional Information & Resources

The thyroid gland, located in the front of the neck, plays an important role in regulating the body’s rate of metabolism. Hyperthyroidism is a disorder characterized by enlargement of the thyroid gland, followed by subsequent overproduction of thyroid hormone and an increase in a cat’s metabolic rate. This condition is the most common endocrine disease in cats, affecting mostly cats in their senior years. In the majority of cases, the thyroid gland enlargement is a benign tumor; less than 1% involve a thyroid gland malignancy.

Short of a thyroid biopsy, there is no definitive way to know if a thyroid tumor is benign or malignant. Thyroid scintigraphy (performed at veterinary specialty hospitals and universities) can provide further information about the affected thyroid glands that may help to differentiate benign versus malignant. Importantly, however, only histopathologic examination (biopsy of thyroid tissue) can confirm a diagnosis of thyroid cancer. Thyroid carcinomas (cancer) can be treated with radioiodine, but much higher dosages and thus longer hospitalization is needed. If we suspect that a patient may have thyroid carcinoma based on physical examination and pre-testing information, poor response to initial I 131 treatment, etc., we will refer the patient to a specialty hospital for thyroid imaging. (Thyroid imaging involves administering a short-acting radionuclide that accumulates in the thyroid tissue and is then visualized with a gamma camera).

Many organs are negatively affected by hyperthyroidism, including the heart. The disease stimulates the heart to pump faster and more forcefully, and eventually the heart enlarges to meet these demands. The increased output of blood from the heart may lead to high blood pressure and, in some cases, heart failure. The liver is also susceptible to damage by overproduction of thyroid hormone, as are the kidneys gastrointestinal tract, and the central nervous system.

The cause of hyperthyroidism in cats remains unknown. Environment and diet have been investigated and may play a role in predisposing cats to hyperthyroidism, though the specific risk factors and mechanisms are unknown. No breed is known to be at increased risk.

The typical cat with hyperthyroidism is middle-aged or older, though the condition has been reported in younger adult cats as well. The most consistent finding among cats with this disorder is weight loss secondary to the increased rate of metabolism. Many cats compensate for this loss by eating more than usual; some hyperthyroid cats may develop a ravenous appetite. Despite the increased intake of food, most cats gradually lose weight. The weight loss can be so gradual that some owners do not notice it until their cat has lost 10–20% of his body weight. Affected cats may also drink more water and pass larger volumes of urine than they did prior to developing this condition. Other physical symptoms may include periodic vomiting, soft stool or diarrhea, and an unkempt hair coat. Some cats develop anorexia as the disease progresses. Behavioral symptoms include elimination outside the litter box, increased irritability, increased activity levels, increased vocalization and other changes.

Systemic hypertension and thyrotoxic cardiomyopathy (heart muscle disease resulting from excess thyroid hormone) are complications that may occur over time in untreated hyperthyroid cats. Both of these conditions are treatable and reversible with appropriate treatment, especially if the conditions are diagnosed at an early stage. Left untreated, congestive heart failure and hypertension complications such as strokes and blindness may occur.

Hyperthyroidism may mask declining kidney function because of the disease-induced increased blood flow to the kidneys. When a cat with underlying kidney insufficiency is treated for hyperthyroidism, renal blood flow returns to normal and the kidney insufficiency may become more apparent. Conversely, hyperthyroidism left untreated can have a deleterious effect on the kidneys as well.

Options for treatment of hyperthyroidism in cats include radioactive iodine therapy, medical management (most often oral medication), dietary management, and surgical removal of the affected thyroid gland(s). Because the large majority of cats with hyperthyroidism do not have cancerous tumor growth, treatment can be completed in most cats using relatively low dosages of radioiodine. (Cats with cancerous tumors will require much higher dosages of radioiodine and often higher dosages of oral medication as well.)

Radioactive Iodine

Radioiodine treatment (RAI or I 131) is considered the gold standard treatment for hyperthyroidism in most cats, particularly in younger cats and in those cats without advanced kidney disease or other concurrent but significant non-thyroidal disease.  It is curative 95% of the time with a single treatment (especially when done earlier in the disease process), and in most cases, treatment with radioiodine eliminates the need for long-term oral thyroid medication. It is the most effective and least invasive way to destroy all of the abnormal thyroid tissue. Veterinary clinics must be licensed to administer radiation therapy. After treatment, patients must be hospitalized until their level of radioactivity has declined to a level that is low enough to allow release back into their homes (usually 2-6 days at our hospital).

A disadvantage of I-131 is the precautions associated with radioactivity needed after treatment once the patient is released from our care.

Why Choose Radioiodine

There are pros and cons for all available treatment options for hyperthyroidism in cats, and there is no "one size fits all" for treating thyroid disease in cats. Options other than I-131 may be more suitable for some patients and/or cat owners, though for the majority of cats and cat owners, the advantages of radioiodine treatment outweigh the advantages of other treatment options, and the disadvantages of radioiodine are few. It is considered the treatment of choice for most patients by veterinary endocrinologists. It eliminates the need for twice daily medication in most cats, it cures (rather than controls) the thyroid condition, and it eliminates the chance that the typically benign thyroid tumor seen in most cats with hyperthyroidism will transform into a malignant tumor. Approximately 20% of cats that have had hyperthyroidism for >4 years will develop suspected thyroid carcinoma (cancer). It is believed that this is due to a transformation from benign to malignant over time.

Radioiodine is successful 95% of the time in effectively curing hyperthyroidism with a single treatment. If hyperthyroidism persists for longer than 3-6 months after treatment, re-treatment with radioiodine is recommended to cure the disorder. Most cats that remain hyperthyroid after the first treatment are cured by the second treatment, though these patients are usually referred for thyroid scintigraphy to help rule out thyroid cancer before a second treatment is done.

Although uncommon, we do occasionally see patients whose hyperthyroidism recurs months to years after radioiodine treatment. This may be suggestive of a new thyroid tumor causing thyroid levels to rise again (and less likely a re-growth of the first tumor that was treated with radioiodine). A second treatment with radioiodine may be needed.

Hypothyroidism Post Radioiodine Treatment

Radiation-induced hypothyroidism (thyroid levels that drop down too low following radioiodine treatment) is a potential sequela of radioiodine treatment. Now that we are using better tests to diagnose hypothyroidism (and as a result we are more actively watching for it post radioiodine), we know that it occurs more commonly than was thought historically. Importantly, based on relatively recent research, we also know that hypothyroidism left untreated can have a negative effect on the kidneys over time. As a result, in addition to more closely monitoring for hypothyroidism post treatment, in recent years we have been using significantly lower and more individually tailored radioiodine dosages than we did in the past. The lower dosages fortunately seem to be just as effective in dropping thyroid levels down into the normal range, while also reducing the potential for post radioactive iodine hypothyroidism. 

Our radioiodine dosages are individualized for each patient based on thyroid levels, tumor size, and severity of symptoms—we do not used a fixed dosage for all patients. The incidence of post radioactive iodine hypothyroidism is currently around 15% in our practice (the large majority of these patients have subclinical or asymptomatic hypothyroidism, only a small minority have clinical or symptomatic hypothyroidism). With higher and ‘fixed one-size-fits-all’ radioiodine dosage protocols, hypothyroidism post treatment occurs with a much higher frequency.

Because it is important to identify hypothyroidism sooner rather than later post treatment should it occur, we recommend blood testing after radioiodine treatment at 1, 3, 6 and 12 months.  Hypothyroidism will self-correct itself in some cats, but if it persists, treatment requires daily oral medication (just as in people). Hypothyroidism is a very treatable disease, but can be more difficult to address in feline patients that are challenging to medicate orally. 

Medical Management

Administration of an oral drug, usually Felimazole (methimazole), can interfere with thyroid hormone production and thus control the effects of the overactive thyroid gland.

The large majority of cats tolerate this drug quite well; however, some cats may react adversely to the drug. Some side effects (vomiting, decreased appetite) may resolve by use of alternate routes of medication administration. More serious side effects (self-trauma from intense itching, significant liver enzyme elevations, progressive anemia, low white blood cell counts, etc.) generally require that the medication be permanently discontinued and alternate treatment options be considered. Because medical management is not curative (blunts thyroid production but does not destroy the tumor), the tumor will continue to grow in most cats. With time, as the tumor enlarges, the cat may become resistant to the thyroid medication, requiring higher and higher dosages for better control, with some cats becoming medication resistant altogether. Unfortunately, these cats that are later in the disease process and with larger tumors are also more difficult to successfully treat with radioiodine as well.

Since medical management of hyperthyroidism is not curative, it does not destroy the abnormal thyroid tissue. Thus, the drug must be given for the remainder of a cat’s life. Oral medication must be administered daily (usually twice per day), and the dosage often needs to be adjusted periodically to maintain normal thyroid hormone levels.

Bloodwork is generally done every three to six months to monitor thyroid, liver, and kidney values but may need to be done more frequently if the thyroid levels are not well regulated or if there are concurrent health issues.

Dietary Management

In late 2011, a prescription veterinary diet, available in both wet and dry forms from Hill’s Pet Nutrition, was introduced for the treatment of hyperthyroidism in cats. Although the exact cause of hyperthyroidism has not been identified, a diet low in iodine has shown potential as a means of reducing elevated thyroid levels. Cats being treated with diet alone must eat the diet exclusively for life.


The fourth option is surgical removal of the affected thyroid gland(s). Because hyperthyroid cats are usually older and because heart and metabolic abnormalities are associated with hyperthyroidism, there is often an increased anesthetic risk involved with this treatment option. Surgery is a more invasive procedure, and postoperative complications may arise. If ectopic thyroid tissue (tissue in abnormal locations) is not detected and therefore not removed during surgery, hyperthyroidism may redevelop. Depending on the patient and the patient’s owner, surgery may be an appropriate treatment option (and it is considered a cure, as is radioiodine), but in most cases, radioiodine is preferable.

The outcome following treatment of hyperthyroidism is usually positive, and most cats have a good chance of returning to an excellent state of health for many years. It is one of the few diseases in older cats that we can treat relatively easily, and even cure (with radioiodine and surgical removal of the thyroid glands), though there are pros and cons of all available treatment options.

No preventive measures are known, but we recommend that middle-aged and geriatric cats have a complete physical examination by a veterinarian every 6 months.

Our goal is to provide cats and their human families with the best radioiodine facility in the Chicagoland area. We are currently the only facility offering this treatment within the city limits.

Every single team member working with your cat truly loves cats—and every one of us enjoys working with cats of all shapes, sizes, and personalities. We recognize that your cat is a beloved member of your family—as ours are for us. We treat your cat like family.

We are an American Association of Feline Practitioners designated Cat Friendly Practice, which means that we have gone the extra mile to assure that we understand cat behavior, and that we individualize the way we handle every single patient based on what works best for that patient. We respect the rights of every cat under our care to be handled with gentle hands and a soft touch, in a quiet setting. When examining or medicating a patient, we move as slowly as is needed for each patient in order to minimize stress. Your cat needs a time out part-way through the examination? We get that – and we respect your cat’s wish to have a time out. We understand cats, and we know that how a cat is, or is not, handled in the veterinary setting is critical in assuring a minimally stressful visit for the patient. We are also not hesitant to administer anti-anxiety medications in order to help patients better acclimate to their temporary hospital surroundings when needed.

Cats are housed in our lead-lined radiation room for the duration of their stay. The radiation area is away from the busier area of the hospital, and it is very quiet. And of course there are no barking dogs!

Each cat is provided with a spacious suite, which includes:

  • Comfortable cushioned bedding
  • Hiding area (a favorite for most cats in a hospital setting because cats feel more secure when they not so visible to sight; or, better stated, when they think they are out of sight!); many patients are more inclined to eat, drink and be cozy when they are "hidden" and not so visible to anyone in the room. Hiding is a very important coping mechanism for cats that are anxious or fearful (which describes most cats in a hospital setting)
  • Separate litter box area (no eating next to the litter box, please!)
  • Elevated benches in all suites so that cats can perch up high if desired (some of our cage suites include a ‘step’ up to the perch, which is helpful for our arthritic patients)
  • Webcams in every cage suite, so that cat owners can log in any time of day to watch their cat

It is important to us that our radioiodine patients are housed in an environment that is enriched and stimulating. Enrichment amenities, which also help to calm the cats while hospitalized, include:

  • Soft music
  • For cats that want to be let out for stretching, petting, playing while hospitalized, we will accommodate as fully as we can, given safety laws that we must follow
  • As much attention as we’re safely allowed to give them!

We provide daily updates on your cat while he/she is hospitalized. Routinely, we may send pictures either via email or text, or we will call you directly with updates, whatever your preference may be.

The doctors and staff are available for consultation after your cat is released from the hospital if you have follow up questions or concerns after your cat is back in the comfort of his or her own home.

Before Your Cat's Stay

Prior to being admitted for radioiodine treatment, all patients are required to have had diagnostic testing completed within the previous 30 days. These diagnostics may be done at our hospital or with your family veterinarian. Required tests include:

  • CBC (complete blood count)
  • Blood chemistries (to check kidneys, liver, blood glucose, electrolytes, etc.)
  • Thyroid hormone (T4) and TSH (canine acceptable) levels; T4 and TSH levels should be run on the same blood sample; T3, free T4 ideal but not required
  • 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 non-thyroid illness, such as heart, intestinal or other issues that we should be aware of prior to I-131 treatment).

In select cases, we may recommend that thyroid scintigraphy be performed prior to radioiodine treatment to help confirm the diagnosis of hyperthyroidism if the diagnosis is less straight-forward based on physical examination and standard thyroid testing. 

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) for hyperthyroidism, these should be discontinued for at least 7-14 days prior to treatment with radioiodine (shorter time frames may be appropriate for some cats). 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 Day of Your Cat's Scheduled Treatment

The morning of your cat’s scheduled treatment, you will have an appointment scheduled for your cat to be examined by one of our radioiodine trained and nuclear licensed veterinarians. During this appointment, the doctor will also provide details 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 discussion, and we are happy to answer any and all questions. Your confidence in our care for your cat is essential. 

Also during this appointment, one of our radioiodine technicians will administer ‘pre-radiation’ medications to your cat. These medications are individualized for each patient, but in general include anti-anxiety and anti-emetic (anti-vomiting) support. It is important that the cat not vomit the radioiodine once it has been administered.

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. (We have plenty of wet and dry options available in the nuclear ward for those cats that struggle to eat when away from home, too). 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 provide a familiar scent which can help reduce any anxiety. (Please note that due to safety guidelines, however, we are not be able to send these items home with you).

We strongly encourage owners to give gabapentin (or other anti-anxiety medication prescribed by your veterinarian) at home 2 hours or so prior to travel to our hospital if possible. We administer gabapentin to most all cats that have not received it at home. Giving the drug at home helps to reduce the stress of travel and thus aids in getting the entire experience off to a better start (assuming that getting the drug into the cat can be done with relative ease).

No fasting is necessary prior to radioiodine treatment, so go ahead and feed your cat on the day of admission. 

During Your Cat's Stay

The radioiodine is administered in the hospital’s nuclear ward 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 cage suite in the nuclear ward. During the hospitalization stay, which is usually 2-6 days, your cat’s radiation levels, heart rate, weight, appetite, stool and urine production, and other vital signs are monitored. Supportive care (appetite stimulants, additional anti-anxiety medication, nausea medication as needed, probiotics should diarrhea develop, fluids to maintain hydration, etc.) will be provided as needed. There may be additional fees in some cases. 

We provide updates to patient owners by email or text daily. Owners are always welcome to call VCA 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.

After Your Cat's Stay

Once your cat’s radiation levels have declined below the maximum allowed by federal and state law prior to being released from the hospital, 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 decayed down to a low enough level for routine dumping in the trash. (Landfills have radiation detectors that will detect radiation and result in a fine if 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.
  • In order to best assure that you are safe from radiation exposure once your cat is home, we recommend that your cat be quarantined or housed in his or her own space (spare bedroom, office space, bathroom, basement, etc.) with all resources (food water, litter, toys) for the required isolation period (one week if no pregnant people of children under age 18 are in the home, two weeks otherwise). We recognize that many city dwellers do not have the luxury of an additional room, so we will work with you to develop a quarantine plan that will keep you safe and still allow your cat to be back in the comfort of home.   
  • Non-pregnant adults are allowed 30-60 minutes per day in the quarantine area with the cat, but cuddling and lap time should be avoided. Petting, playing with the cat, etc. is fine and likely welcomed by the cat!  
  • Children under the age of 18 or pregnant women must not have any contact with your cat, or with your cat’s food and water 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. (Additional charges would apply).
  • Wear disposable gloves (we will provide a few pairs of gloves or you at release) when handling litter box excrement and when petting your cat. Scoop the litter twice daily for 14 days after release. Use a plastic liner in the litter box for this 2 week period. Either flushable or non-flushable litter can be used during this period of time. 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).
  • 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 radiation-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 for 81 days (after the 2-week period of collection) in order to prevent radioactive litter from entering the landfill.
  • 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. Keep dogs in the home away from your cat's litter box!

Our front desk Client Service Coordinators are happy to provide current pricing upon request. Our 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/appetite stimulants/basic supportive care required while hospitalized. Any additional treatments needed during the hospitalization stay would result in additional fees. Boarding beyond the initial hospitalization period (i.e., after your cat is eligible for release) would also result in additional fees. While our treatment fee is a higher upfront cost compared to other hyperthyroid treatment options, it is relatively equivalent with other options over the lifetime of the cat. Radioiodine treatment (after the first year post treatment) generally results in fewer thyroid blood tests for the remainder of the cat’s life, which makes the treatment more cat-friendly from the patient’s point of view as well.

VCA Cat Hospital of Chicago accepts cash, checks, all major credit cards, Apply Pay, and Care Credit. 

Please note: Because we must order the dose of radioiodine from our nuclear pharmacy the week before radioiodine is administered, and the dosage is tailored specifically for your cat, cancellation of a scheduled appointment less than 96 hours before the appointment time will result in a charge of $375. 

Pre-Treatment Diagnostics & Patient Evaluation

Pre- I-131 patient examination and testing can be done at VCA Cat Hospital of Chicago or through the referring veterinarian’s hospital clinic (former recommended if pre-testing deadlines cannot easily be met). Required pre-radioiodine diagnostics include the following diagnostic tests within 30 days of treatment, preferably from a major veterinary laboratory:

  • CBC
  • Chemistry Profile
  • T4/TSH/T3/free T4 (T4 must note a number; i.e., ‘>4’ from an POC machine is not sufficient; cTSH acceptable; T4/TSH levels should be run on same sample; T3/free T4 recommended but not required)
  • Urinalysis, +/- urine culture (urine culture if suspicion for UTI)
  • Blood pressure
  • Chest radiographs (minimum 2 views, ideally 3 views)
  • Abdominal radiographs +/- abdominal ultrasound (applicable for patients suspected to have, or known to also have, significant non-thyroidal abdominal disease)
  • Echocardiogram (if suspicion for moderate to severe heart disease, and/or if concern that cat may experience CHF while hospitalized post I-131 treatment). The presence of a heart murmur alone in an asymptomatic patient does not require that an echocardiogram be done unless the referring DVM feels it would be appropriate to do so.

If the cat has been on methimazole or other medical management treatment (PTU), prior to radioiodine administration, we require the cat to have been off the medication for at least 7-14 days prior to I-131 treatment (or, if on YD diet, we ask that the cat have been off the Hills Y/D diet for 8 weeks), and T4 and TSH levels at least 7 days after cessation of methimazole/YD.

Previous records, including the information above, as well as date of hyperthyroid diagnosis, T4 when initially diagnosed and other pertinent patient information (EMR/patient medical record to include weight history, presence or not of a thyroid slip, approximate size of slip if present, pertinent surgeries, communication with owner regarding hyperthyroidism/radioiodine, all laboratory tests since hyperthyroidism diagnosis whether on/off methimazole or Y/D when applicable, etc.) can be faxed to VCA Cat Hospital of Chicago at 773-207-5090.