Urinary stones in cats – what is important?

Cats are by nature desert inhabitants. Therefore they do not drink very much. As a result of not taking in much liquid, their urine is often very concentrated. Depending on the composition of the urine and the presence of other risk factors, such as unbalanced diet, being overweight or stressed, crystals and urinary stones can be formed.

The formation of crystals and urinary stones is particularly dangerous for male cats, i.e. tomcats. Their narrow urethra can very easily become blocked. A complete blockage of the urethra is not only extremely painful, but can also become lethal as the cat is then no longer be able to pass urine. This is always a life-threatening emergency that requires immediate medical attention.

FLUTD syndrome in cats

Illnesses in the urinary tract are summarised under the term FLUTD (feline lower urinary tract disease). A FLUTD, which may firstly occur without crystals or urinary stones forming, needs to be paid attention. This is due to infections facilitating the formation of crystals in the bladder, which then can form urinary stones following the accumulation of more crystals.


FIC (feline idiopathic cystitis) is a new bladder syndrome, which affects only female cats. This appears as a culmination of currently unknown factors causing a non-bacterial, sterile bladder infection, which can also predispose the affected cats to urinary stones.

Different urinary stones: Struvite vs oxalate

Urinary stones can have various compositions. While in the past predominately struvite stones occurred, today we are seeing an increase in oxalate crystals and oxalate stones. These normally consist of calcium oxalate and can have very sharp spikes on their surface. The difference is that struvite stones can normally be passed following a change to the cat’s diet in order to alter the pH level of its urine. Oxalate stones, however, cannot.

Diet and other factors

Today, good cat food contains a balanced composition of minerals to prevent urinary stones. However, even cats who have an optimal diet (high-quality protein and not too much vitamin D as this causes the calcium levels in the blood to become too high and then creating calcium oxalate stones) can suffer from stones. Some breeds are predisposed to this, such as Persian cats and British Shorthair. But all other breeds and normal housecats (European Shorthair) can also be affected, particularly tomcats (see above). One of the most important preventative measures is to encourage the cat to take in more water, for example by putting up a water fountain or by taking advantage of some cats’ habit of drinking from the tap. Liquid cat milk (e.g. GimCat Milk) or liquid-based, attractive snacks (e.g. GimCat Pudding) also increase water intake. A balanced diet of moist and dry feed is also advisable.

A very important point is the pH level of the urine. Delicious pastes have recently been introduced to achieve the correct pH level. These special pastes are a very good option as some cats do not like eating special ‘urinary’ food.

Another significant cause is stress. Cats are very sensitive to changes in their surroundings. It is not always easy for cat owners to recognise that their cat is stressed. This is why a stress analysis should also take place if treatment is sought for a FLUTD or urinary stone problem.

Symptoms, treatment, prevention

If your cat often visits its litter box and mews while doing so, or you find red-coloured litter, this could indicate FLUTD/urinary stones. Then you must take your cat to see the vet as soon as possible. Some cats with FLUTD or urinary stones start to have accidents because they associate going to the toilet with pain. Unclean toilet habits therefore should not immediately be attributed to behavioural problems, rather the cat’s urinary tract should always be examined first of all.

If you cannot find any signs of visits to the toilet, and you have a tomcat, it could be an emergency and you should immediately – whether in the evening or at the weekend – contact a veterinary surgery or clinic.

Diagnosis and therapy

Diagnosis of FLUTD, FIC and/or urinary stones consists of examining a blood or urine sample, X-rays at two levels and an ultrasound scan. The kidneys could also start suffering, to find out the SDMA value also has to be measured. This thorough, initial diagnosis is very important, particularly as recurrence is frequent in tomcats especially.

The aims of acute therapy are rapid pain alleviation and the swift removal of the crystals or urinary stones. A catheter must be used for tomcats to flush out blocked urethras and intravenous fluid therapy is also important. In some cases, an operation may be necessary.

Another important thing to note is that, if a small stone has become lodged in the ureter, i.e. caught between the renal pelvis and bladder, it will not necessarily be painful but the affected kidney may nevertheless be in danger. This is why two X-rays at two different levels are necessary (highest possible resolution of digital X-ray) – only then can the ureter be seen. In order to save the kidneys and the cat itself, modern technology now allows a bypass to be introduced between the kidneys and bladder. This bypass operation, however, is currently only offered by a handful of animal clinics.

The long-term management aims to prevent recurrence and, in order for it to work, must include all of the factors mentioned above.