Cat Thyroid Center
FAQs and Explanation of Testing
Why and what is “clean” lab work?
When patients have been on anti-thyroid medication, supplements, or Hill’s y/d diet for more than 2 months, “clean” lab work is necessary to help accurately determine their treatment dosage.
Since the overactive nodule can continue to grow while on these treatments, the baseline T4 may change significantly. These changes can directly influence the amount of radioiodine given.
Dependent upon their current treatment, patients must discontinue for a certain timeframe prior to new testing.
Methimazole/Felimazole 14 days
Hills y/d diet 3 weeks
Thyroid supplements- please call our facility for guidance. Some require up to 6 weeks in order not to interfere with results of testing and treatment.
By getting a current thyroid value (while off treatment) we can more accurately dose the I-131 and achieve better treatment outcomes.
Why a reference lab vs in house testing?
An accurate and absolute value is critical to determine an accurate treatment dosage.
We have seen significant variations in T4 values between in house and reference labs.
In addition, “greater than” values make it impossible to treat a patient confidently. For example, a T4 of >8.0 may be 8.1, or 12, or 35. The actual value will help minimize the chances of treatment failure or permanent hypothyroidism after treatment. Of note -
Antech will report a T4 value up to 40 mcg/dL
Idexx will report a T4 value up to 24 mcg/dL (may add a T4 by RIA to obtain a value up to 40)
Zoetis will report a T4 values up to 15 mcg/dL (they will dilute further upon request)
When is a Free T4 (ED) warranted?
The T4 is equivocal (within the top quarter of the reference range)
The T4 is in the high end of the reference range or just above normal.
These patients may or may not be symptomatic.
A free T4 by equilibrium dialysis is strongly preferred, when measuring a fT4 is indicated.
These patients may also need to be retested in several weeks or months to confirm the diagnosis unless a thyroid nodule is palpable.
Why are radiographs recommended?
Radiographs are a non-invasive tool to screen for concerns not apparent on lab work. Most of our patients are seniors and may have concurrent medical issues. We routinely find masses and other abnormalities that may warrant a change in the treatment plan altogether. Occasionally masses or nodules are found in the chest that may or may not be associated with hyperthyroidism. This can also affect the dosage.
Radiographs can give the client more information on their pet’s health so that they can make an informed decision on whether they would like to move forward with treatment. Many times, we move forward and cure the hyperthyroidism while the owners are aware that other concerns may need addressed.
Renal Disease Screening
As we treat primarily senior and geriatric cats, many of our patients have some stage of renal disease.
Hyperthyroidism makes IRIS staging difficult as active hyperthyroidism can mask the extent of renal dysfunction. The more information on renal function we have, the better we can prepare owners for what to expect as far as renal disease management post treatment.
However, there is no way to predict the development of renal disease with 100% accuracy.
Typical pre-treatment renal evaluation would include BUN, Creatinine, SDMA, and urinalysis.
Post-treatment labwork is recommended ONE and THREE months after I-131 treatment – this testing should include at a minimum the weight, T4, BUN, Creatinine, SDMA, and urinalysis.
Consider Blood Pressure, CBC, full chemistry, and often a cTSH in addition.
Thyroid Nodules
If you are able to palpate a thyroid nodule, please include this information in the medical notes!
A size comparison is also beneficial. (ex. pea sized, 6mm, …). This information helps “fine tune” dosing. We know this can be tricky, even on the best of patients!
Each Patient is Unique
While we have guidelines for preadmission, each patient is unique!
Our goal is to make the process as easy as possible.
When your patient doesn’t “fit the mold,” or if you have any questions, please call or email us!
We are happy to help!
Patients with Gallop Rhythm or Murmurs
We find patients with abnormal heart rhythms and murmurs due to the extremely high heart rates, sometimes exceeding 300 bpm. This tachycardia can be controlled with cardiotropic medications such as Atenolol until the radioactive iodine takes effect. Usually the heart medications can be discontinued within 3-4 weeks after treatment and the heart rate will be almost normal. Sometimes the murmurs improve or disappear, but not always.
Professional Discount to Veterinarians
We offer a professional discount to licensed veterinarians, Veterinary staff, and qualifying feline rescue organizations. Please call for information.
If you have questions regarding the treatment of Feline Hyperthyroidism and how we can help your cat, visit the contacts page and fill out the Inquiry Form and a representative will contact you.
