Kidney stones are an uncommon problem in cats (unlike bladder stones, which are relatively common).
The majority of cases I see are diagnosed as an incidental finding when the animal is radiographed for another reason. This is because it is rare for kidney stones to cause symptoms, and the majority of cats that have them don’t show signs.
There are, of course, exceptions — I once treated a cat with a painfully swollen kidney as a result of a stone blocking drainage to her bladder.
It is perhaps surprising that kidney stones don’t cause more discomfort than they do, and as already mentioned, the majority of kidney stones are found by accident when the patient is being X-rayed for another problem.
The rare cases associated with pain happen when the stone passes out of the kidney and becomes lodged in the ureter, the tube that drains urine from the kidney to the bladder. Back pressure builds in the kidney, which then swells and becomes painful, and occasionally some blood appears in the urine.
This phase usually only last a few hours, and the cat is restless and uncomfortable until the stone is passed. My little cat was unusual in that she was in severe pain, but she responded well to pain relief and intravenous fluids and is now back to normal.
In this video, veterinarian Dr. Carrie Burhenn discusses symptoms cats may experience:
The body is basically a big chemistry set, and the body’s chemicals combine with minerals in the diet to form crystals, which can stick together and form grit, gravel and stones. Above a certain size, this grit gets stuck in the filter of the kidney, where it acts as a focus (a bit like grit in an oyster) for more minerals to be deposited around it.
The commonest stone in the kidney is made up of calcium oxalate. This is a radio-dense material and shows up on radiographs, hence the surprise the vet sometimes gets when taking X-rays of the pet for some other reason.
The minerals in the commonest stone show on an X-ray, but some less common types do not. If your vet suspects a kidney stone is causing a problem, then an ultrasound scan should find it, no matter what mineral the stone is made from.
If the cat has discomfort passing a kidney stone, then pain relief, intravenous fluids and antibiotics are necessary to help him through this difficult period.
In rare cases, a specialist procedure may be needed, where a laser blasts the stone into smaller pieces that can be passed easily.
Preventing Kidney Stones in Cats
A cat that has grown 1 kidney stone is likely to develop others in the future, and so prevention is important.
Factors that make stone formation more likely are the pet being overweight and not drinking enough. Fat cats are more likely to be lazy and not get up to empty their bladders as often. This means the minerals have longer to brew in the urinary tract and form into stones.
Likewise, cats that don’t drink tend to build up minerals, making it easy for stones to form. To encourage your cat to drink more, try a water fountain and put wide water bowls around the house. Your vet may suggest a change of diet as well.
- Clinical Medicine in the Dog and Cat. Schaer. Publisher: Manson Publishing.
This pet health content was written by a veterinarian.