Thursday 14 August 2008

Feline Kidney Stones

three healthy cats
Healthy cats - photo by Ferran.

Feline kidney stones are rare, perhaps very rare in cats. In fact according to Drs Carlson and Giffin the authors of "Cat Owner's Home Veterinary Handbook", it is almost unheard of.

Another book designed for "cat people", "The Veterinarian's Guide to Your Cat's Symptoms" by Drs Garvey, Hohenhaus, Houpt, Pinckney, Wallace and Elizabeth Randolph, doesn't make reference to them in the index and I couldn't find anything in the book (although I may have missed it).

And they are referred to in passing under the heading, "Obstructive Urinary Tract Disease" in the book, "Veterinary Notes for Cat Lovers" by Dr. Trevor Turner and Jean Turner VN. The authors refer to "in rare cases, true stony Uroliths......". Uroliths are crystalline material commonly called stones, by the way.

A more technical term for stones is "struvite stones" or "struvite crystals". Struvite is an ammonium magnesium phosphate mineral. Struvite is caused by a bacterial infection that hydrolyzes urea to ammonium. When something is hydrolyzed is undergoes the process of hydrolysis. Hydrolysis is a chemical reaction (I'm going to stop there.......!). The stones are magnesium/ammonium/phosphate based material and look like salt in terms of size.

I am going to presume that people searching for feline kidney stones are in fact searching for information about urinary tract stones generally and which are a part of the symptoms of Feline Urologic Syndrome (FUS). The presence of stones causes the cat to strain when urinating, urinate in the wrong place, urinate small amounts, go frequently, urinate bloody urine and lick themselves a lot. This is because they plug the passage of the urine. Other substances can also plug the urinary tract such as mucus and white blood cells.

Bladder stones in cats are, it seems less rare, and are related to FUS. There is a greater chance of stones forming in the bladder that is permanently infected (bacterial infection) and a bladder that is partially blocked. The symptoms are similar to FUS.

Obviously initial treatment for feline kidney stones (more accurately urinary tract stones as kidney stones are very rare) must be supervised by a veterinarian. Diet, it is suggested, can help to dissolve the crystalline stones post veterinarian treatment (diet is also central to prevention). Drs Carlson and Giffin say that Hills Prescription Diet s/d dissolves stones or parts of stones not dealt with a the vets surgery. This is a low magnesium cat food (also more acidic) and could be called urinary tract cat food as it helps to keep the urinary tract healthy. A cat should remain on the diet for 1-2 months and an improvement in health will be seen within 7 days.

Clearly the best course of action for feline kidney stones (or more commonly urinary tract stones) is to take preventative steps, which begs the question, "what causes feline kidney stones?" The causes are cat diet related and a person I have mentioned before on this website, Dr. Hodgkins (author of Your Cat) believes that the increase in incidence of FUS is due to the shift to dry cat food over the past 10-15 years (i.e. convenience foods for cats). Quality wet cat food is better. Better still, but rarely contemplated unless you're a cat breeder, perhaps, is natural raw cat food prepared specially but this takes skill as supplements are needed such as Taurine.

Drs Carlson and Giffin go down the more conventional route than Dr. Hodgkins in respect of preventative steps. They say that some underlying causes are a diet that is high in magnesium content, dirty litter trays (forcing some cats to retain their urine), lack of exercise (overweight cat) and reduced water intake. Reduced water intake means that the urine becomes static with an increased likelihood of bacterial infection. A reduced water intake may be due, in part, to the need to take in more water if the diet is exclusively dry food and some cats will not compensate sufficiently and drink more water. Wet cat food contains high levels of water in contrast.

Drs Carlson and Giffin agree with Dr Hodgkins that another cause appears to be dry cat food. My vet recommended supplementing my cat's diet with fish (I microwave it from frozen) and add water to it. Cats like to lick up the fishy water increasing water intake and flushing the urinary tract, keeping it more healthy. Interestingly an early vet that I saw (before my cat suffered from FUS) recommended Hills l/d dry food permanently. This I believe contributed to her getting FUS. She has been free of it since eating more wet food and fish and added water.

In conclusion, the risk of contracting FUS and feline kidney stones can be substantially reduced if our cat eats the right food, meaning (for most of us) quality wet food low in magnesium and acidic. I tend to compromise and feed low magnesium cat food (say Hills Science Diet Feline) and boiled or microwaved fish with water added plus the occasional tuna and water and other standard wet foods. I have tried to source prepared raw cat food without success. I also change her water bowl very regularly - 3 times daily (in fact she prefers to drink from a glass which is some distance from the food).

There may be other underlying causes and complications, which only a good veterinarian can resolve.

Feline Kidney Stones to cat health problems

Feline Kidney Stones - Sources: as mentioned in the text.
Feline Kidney Stones - Photo - published under creative commons license = Attribution-NonCommercial-NoDerivs License


  1. Hi, Thanks for the comment, it is appreciated.

  2. Need to know the type of stone - calcium or struvite. The acidic diet helps the struvite problem but increases the problem with calcium type stones. There is information on this at the Winn Feline Foundation site - the Winn Foundation provides support for research into feline health issues, and is not associated with a cat food company.


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