Veterinary Services

Feline Hyperthyroidism

Hyperthyroidism is a common condition in older cats where the thyroid gland produces too much thyroid hormone.

What is Feline Hyperthyroidism?

Under normal conditions, thyroid hormone levels are tightly controlled by the brain in a feedback loop. In hyperthyroid cats, however, abnormal thyroid tissue (benign tumor tissue) produces hormone independently—ignoring the body’s normal regulation system.

This leads to elevated hormone levels that can affect nearly every system in the body.

Common Effects of Hyperthyroidism

Weight loss despite a good or increased appetite
Muscle loss
Increased activity or restlessness
Elevated heart rate and blood pressure
Potential strain on the heart and kidneys



What is I-131 Treatment?

Radioactive iodine (I-131) is considered the gold standard, curative treatment for feline hyperthyroidism.

It works by selectively targeting the abnormal thyroid tissue while sparing healthy cells.



How It Works

The radioactive iodine is absorbed only by overactive thyroid tissue
The abnormal (tumor) cells take up the iodine and are destroyed
Normal thyroid cells—temporarily inactive—are preserved
Over time, normal thyroid function is restored in most cats

Because of this targeted approach, most cats:

Do not require lifelong medication
Experience a true cure of their hyperthyroidism



Tests needed within 30 days before I-131 treatment:

Blood Tests Required:
- Complete Blood Cell Count (CBC)
- Serum chemistry profile, including electrolytes
- Total T4 (not free T4) and TSH (cTSH if feline TSH not available)
Urinalysis – including urine-specific gravity
Chest X-rays: Three views (right and left lateral and ventrodorsal views)
Blood Pressure
Vaccinations: Rabies and Feline Distemper must be up to date
Recent dose of flea and tick treatment; if not, this can be applied on day of admission
Some cats may need additional tests based on their individual needs.

What to Expect After Treatment

At-Home Quarantine Care

After your cat goes home, a short period of quarantine is required to ensure radiation levels continue to decrease safely. We will guide you through this process so you feel confident and prepared.

Length of Quarantine

7 days if there are no children under 18 or pregnant individuals in the home
14 days if children or pregnant individuals are present

During this time, your cat will need to stay in a separate room away from the rest of the household.

Daily Interaction Guidelines

Your cat can still receive love and attention during quarantine – just with a few precautions:

Each non-pregnant adult may spend up to 30 minutes per day in the room
You can feed, play, and provide TLC during this time (at arms length)
Maintain about an arm’s-length distance (rather than holding your cat on your lap)

Litter & Cleaning

Flushable litter should be used during the quarantine period
If flushing is not possible, used litter must be stored safely for 81 days before disposal
Wash hands after handling litter, food bowls, or any accidents
Routine cleaning with soap and water is effective

We’re Here to Help

Quarantine can feel intimidating at first, but most clients find it very manageable with a little preparation. Our team will walk you through everything before discharge and is always available if questions come up at home.