Bladder stones in cats – why does identifying the type of urolith change the entire treatment approach?
- Ecommercy
- 2026-09-21
- 15:52
- 0 comments
Urinary stone disease in cats is not a single disease entity and should not be managed according to a single protocol. The presence of crystals, urinary “grit”, or even a stone in the bladder is only the starting point for diagnosis. The composition of the urolith, urine pH and specific gravity, the presence or absence of infection, and the patient’s overall clinical condition all determine the appropriate treatment and nutritional management.
This was the focus of the webinar “My cat has bladder stones. What next?”, presented by vet Magdalena Firlej-Oliwa. The webinar focused primarily on bladder stones in cats, their diagnosis, differentiation of the most important types of uroliths, and the role of nutrition in treatment and the prevention of recurrence.
Full webinar recording:
Finding a bladder stone is not a complete diagnosis
One of the key conclusions from the webinar is that “urolithiasis” should not be treated as a single diagnosis. Knowing that a stone is present in the bladder is not enough to plan targeted treatment. When uroliths are surgically removed, analysing their composition should be an important part of further management, as this information is essential for planning appropriate prevention of recurrence.
This is particularly important in nutritional management. A diet that may be beneficial for a cat with struvite stones will not automatically be appropriate for a patient with calcium oxalate or ammonium urate stones. Similarly, the presence of crystals in urine sediment alone should not automatically lead to the introduction of an acidifying supplement or a urinary diet.
In clinical practice, the key question is therefore not simply: “Does the cat have bladder stones?” but rather: what type of urolithiasis are we dealing with, and why did it develop?
One strategy that applies to most patients: urine dilution
Although management depends on the type of urolith, one factor is common to most urological patients: increasing water intake and consequently reducing urine concentration.
A greater urine volume means lower concentrations of substances that may crystallise. In the webinar, urine dilution was highlighted as a fundamental element in the prevention of different types of urolithiasis.
This is particularly important in cats because of their natural drinking behaviour. In practice, feeding a high-moisture diet remains the primary nutritional strategy. Wet food can increase total water intake in a much more physiological way than attempting to compensate for dry feeding with water consumed from a bowl.
Depending on the patient’s tolerance, additional water can also be added directly to meals. However, it is important to remember that substantial additional water intake may affect the interpretation of urine specific gravity. If the purpose of testing is to assess the kidneys’ natural urine-concentrating ability, the type of diet and the amount of water added to meals should be taken into account when interpreting the result.
Urine pH: a result that can easily be overinterpreted
One of the most practical topics covered in the webinar was the interpretation of urine pH. It is an important parameter, but one that is highly sensitive to the conditions in which the sample is collected and stored.
Urine pH should be assessed as soon as possible after collection. A sample left for several hours may no longer accurately reflect the environment previously present in the bladder. During storage, urine pH may change and crystals may precipitate secondarily.
This has direct therapeutic implications. Introducing an acidifying supplement on the basis of an unreliable result may shift the pH too far towards acidity and create conditions that favour another type of crystallisation. The webinar highlighted cases in which prolonged urine acidification resulted in very low pH and the formation of calcium oxalate crystals.
Urine pH should therefore not be interpreted in isolation from urine specific gravity, sediment findings, the clinical picture, diet, and the method and timing of sample collection.
Struvite stones in cats: canine protocols should not be applied automatically
Struvite urolithiasis is a good example of why species differences matter. In dogs, struvite stones are very often associated with urinary tract infections. In cats, however, struvite urolithiasis is most commonly sterile. The presence of struvite alone therefore does not justify automatically starting antibiotic treatment. Infection should first be confirmed.
Factors that promote struvite formation in cats include concentrated urine, a pH conducive to crystallisation and an unfavourable ionic composition. Diet, water intake, body weight and the frequency of bladder emptying are also important.
In appropriately selected patients, conservative management and dissolution of the stones may be possible. However, the cat still requires monitoring. As a urolith becomes smaller, it may reach a size that allows it to enter the urethra, creating a risk of obstruction. Larger uroliths are more likely to require surgical intervention.
Calcium oxalate: diet cannot dissolve an existing stone
Calcium oxalate stones require a very different approach. Once formed, an existing calcium oxalate urolith cannot be dissolved by changing urine pH or diet. Nutrition therefore plays primarily a preventive rather than therapeutic role.
The risk of crystallisation depends, among other factors, on the availability of calcium and oxalate and on urine concentration. Importantly, prevention of calcium oxalate urolithiasis cannot be reduced simply to manipulating urine pH. If the appropriate substrates are present and the urine is highly concentrated, calcium oxalate crystals may form across a range of pH values.
Once again, increasing water intake and reducing urine specific gravity become central elements of management. The patient’s entire diet, supplementation and any disorders that may affect calcium and phosphate metabolism should also be assessed.
The webinar also addressed magnesium and vitamin B6 supplementation. However, evidence for their preventive effects in animals is not sufficiently conclusive for these supplements to form the basis of management. Appropriate hydration, control of factors affecting RSS and a properly balanced diet should be given much greater priority.
Ammonium urate: crystals that should extend diagnostics beyond the urinary tract
Identifying ammonium urate is particularly important because its pathophysiology differs considerably from that of typical struvite or calcium oxalate urolithiasis.
The webinar highlighted the association between this type of urolithiasis in cats and metabolic disorders, particularly abnormal hepatic blood flow associated with a portosystemic shunt. In a young cat with stones or crystals, the presence of ammonium urate should therefore prompt investigation for an underlying systemic cause rather than simply a change in diet.
In these cases, nutrition plays a supportive role. Treatment should primarily target the underlying disease. If the patient is not eligible for surgical treatment, one of the aims of nutritional management may be to reduce ammonia production, which involves controlling protein intake. In cats, however, this requires particular caution because excessive protein restriction may lead to loss of muscle mass.
This is also an example of a situation in which routine use of an acidifying diet may be inappropriate. In the case of ammonium urate, the webinar specifically emphasised that the urine should not be acidified.
A “urinary diet” is neither a diagnosis nor a universal treatment
In everyday practice, it can be tempting to follow a simple rule: crystals in the urine mean that a urinary diet is needed. However, this approach can lead to mistakes.
The term “urinary” covers products that work through different mechanisms, including modification of mineral intake, alteration of urine pH and increased urine volume. This does not mean that every urinary product is appropriate for every type of urolithiasis.
Diet selection should be a consequence of diagnosis, not a substitute for it. Particular caution is required with long-term urine acidification without a confirmed indication.
The same principle applies to supplements. Several products given simultaneously may provide the same minerals from different sources. In a patient with urolithiasis, it is therefore important to assess not only the name and stated purpose of each supplement, but also the overall composition of the diet and all additional products being administered.
Urethral obstruction remains an emergency
Bladder stones can lead to urethral obstruction, particularly in male cats. In such cases, the problem is no longer limited to inflammation or discomfort caused by the presence of a urolith – the cat is unable to empty its bladder.
The webinar highlighted the development of hyperkalaemia, which can lead to serious cardiac arrhythmias. An inability to urinate should therefore be treated as a life-threatening emergency.
Haematuria, frequent visits to the litter tray, passing small amounts of urine, dribbling, vocalisation during urination, pronounced straining or urinating outside the litter tray all require diagnostic investigation. A complete inability to pass urine requires immediate veterinary attention.
Patients with a history of urolithiasis still require monitoring
Removal or dissolution of a stone should not be regarded as the end of treatment. Follow-up urinalysis, ultrasound examinations and preventive measures tailored to the type of urolith remain important.
This is particularly relevant in cats with calcium oxalate stones, as the webinar highlighted their high risk of recurrence and the frequent presence of concurrent renal abnormalities. These patients require long-term monitoring even if they remain asymptomatic after treatment.
Follow-up assessment should include a properly collected urine sample analysed promptly. Depending on the individual case, diagnostic imaging may also play an important role. Blood tests alone cannot diagnose urolithiasis, although they may reveal its consequences, including acute kidney injury.
From identifying crystals to treating the patient
The key message of the webinar is the importance of an individualised approach. Urinary “grit”, crystals in the sediment or elevated urine pH alone are not sufficient grounds for implementing a single universal protocol.
Struvite, calcium oxalate and ammonium urate uroliths differ in their mechanisms of formation, treatment options and nutritional management. Appropriate diagnosis should therefore precede changes to diet and supplementation.
At the same time, one principle applies to almost all of the cases discussed: increasing water intake and reducing excessive urine concentration. This is one of the most important and broadly applicable preventive strategies in feline urological patients.
A full discussion of the condition, including practical examples, interpretation of urinalysis results and answers to participants’ questions, is available in the webinar “My cat has bladder stones. What next?” with vet Magdalena Firlej-Oliwa.