Vet School Interview [I131 Details]

9 Dec

Signs of hyperthyroid in cats:

-suddenly excessively vocal

-rough hair coat

-very active

-behavioral changes ie aggression, anxiety, unsettled

-losing weight despite eating more food


-rapid heart rate

1.  Most cats are diagnosed at 8 years or older (avg of 13 yrs)

2.  Existing kidney problems complicate hyperthyroid treatment

—–A.  Since hyperthyroid can mask kidney disease, I131 can show kidney failure irreversibly.

———-A1.  Best way to avoid such a situation is to do blood work and specifically a urine specific gravity prior to hyperthyroid treatment.


.5.  *food-may ONLY eat the Y/D for life.  Must still check blood levels.

*very new treatment and long term results are not available.  I would like to see how many cats do on it before coming to any conclusions about the effectiveness or potential side-effects.

1.  lifelong Methimazole PO or PLO

—–A.  must consistently give daily to three times daily pill or pay more for PLO

———-A1.  Can cost $2/day, which adds up over a lifetime.

—–B.  side-effects in 20% of cats

———-B1.  lethargy, anorexia, vomiting, liver failure.

2.  Thyroidectomy-surgical removal of diseased thyroid tissue

—–A.  Sx can be risky in a geriatric patient who may have heart or kidney disease.

—–B.  Parathyroid glands are situated very close to the tyroid

———-B1.  Parathyroid maintain normal Calcium & Phosphorus levels

———-B2.  Can be disrupted, damaged, or destroyed during sx
—————B2a.  May need lifelong supplementation

3.  I131 Radioactive Iodine Therapy

—–A.  An SQ inj of I131 goes straight to the bloodstream.

———-A1.  Only the thyroid gland is affected by radioactive Iodine inj

—–B.  Attaches to thyroid gland and neutralizes overactive tissue, leaving normal intact.

———-B1.  Only tissue that produces T4 (thyroid hormone) utilizes Iodine in the body.

———-B2.  Overactive thyroid cells require more Iodine to produce more T4

—————B2a.  So the I131 is absorbed within 24 hours of the inj.

—–C.  Normal thyroid tissue doesn’t produce t4 in a hyperthyroid cat.

———-C1.  Once the abnormal tissue is gone, the normally functioning thyroid is stimulated to produce T4.

—–D.  one injection is 95% effective.  If a second injection is needed–it is 100% effective.

———-D1.  3mo post inj BW req to make sure it worked

———-D2.  0.25% of I131 treated cats become hypothyroid

—————D2a.  Of those, even fewer need lifelong thyroid supplement


I am a certified radiology worker, as part of my job at Cat’s Meow.  I have to watch the radiology video yearly, and also wear a docimeter to measure radiology I’m exposed to on the premises.  Concerning is that my monthly readings are always highest.  Even higher than the vets who are touching the Radioactive Iodine, messing with the cats, and cleaning the urine and room afterward.  I must have a higher than average radiation in my body–I blame Nevada, and possible toxins in the environment I grew up in for that. . .  Anyway, here’s my job procedure related to the I131:

1.  In isolation take cotton-tipped swap and do a sweep

—–A1.  Use Geiger Counter to read levels

———-A1a.  Log 3 different areas & background in the notebook.

2.  Set up cages

—–2A.  Disposable pee pads as kennel liners and on floor under

—–2B.  Trash bags over litter-boxes & generous amt dust-free litter

—–2C.  Water, own food, and cage card

—–2D.  Write animal tracking info in notebook

3.  Vet calculates doses and checks in radioactive Iodine.

4.  Gown and glove then give SQ inj under hood.

5.  Cat is isolated for 3 days.

—–5A.  Unbound Iodine (up to 90%) is excreted through urine w/in first 2 days

—–5B.  When cat scans w/Geiger at a safe/legal level, allowed to go home.

6.  Owner instructed

—–6A.  not to be excessively close to cat

—–6B.   To flush litter or save it for 6 mos if they have septic

—–6C.  Given a certificate for ride home, b/c police can ticket you for having radiation in the car.

7.  Everyone who enters radiation room or has contact w/cat post inj does bioassay w/in 3 days.

—–7A.  Check background, scan 3 places on neck

———-7A1.  Trouble if person’s neck scans (substantially) higher than background.

Results of I131:

75% of cats will have normal thyroid function within a week!

90% are normal in a month

95% of all cats treated with I131 have normal thyroid values within 3 mo.

Nearly 100% of cats attain normal thyroid values with a 2nd inj.

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