CONDITION
Urinary Stones (Urolithiasis)
Urinary stones are mineral crystals that form inside the bladder or, less commonly, in the kidneys or the tubes connecting them. They vary in size from sand-like grains to pebbles, and their composition differs: some are made of struvite, others of calcium oxalate, urate, or rarer minerals. The type of stone influences how it behaves and what may help manage it. Many owners notice straining to urinate, frequent small puddles, blood in the urine, or signs of discomfort when their dog or cat tries to pass water. In male cats and small male dogs, a stone can lodge in the urethra and obstruct the flow of urine entirely, which tends to show as repeated straining that produces little or no urine. A complete blockage is life-threatening and, in cats, can be fatal within 2 to 3 days without treatment. Some animals carry stones without obvious signs, and the stones are found during imaging for another reason. This page explores what urinary stones can look like in daily life, what drives their formation, how they are identified through urine tests and imaging, and the range of approaches, from dietary adjustment to surgical removal, that may be considered depending on the stone type, size, location, and the animal's broader picture.
Why this matters now
Urinary stones can develop at any age, though certain stone types have age predilections. Calcium oxalate stones are more common in middle-aged to older animals, while struvite stones in dogs are often associated with urinary tract infections and can occur at any age. Certain breeds are genetically predisposed: Dalmatians to urate stones, Miniature Schnauzers to calcium oxalate, and Bichon Frisés to multiple stone types. In cats, urinary stones account for around 10 to 15% of cases of feline lower urinary tract disease (FLUTD), which is seen more often in middle-aged, neutered, overweight, indoor cats. The development of stones may be gradual, with crystals forming and aggregating over weeks to months before clinical signs appear, or may present acutely if a stone moves to obstruct the urethra.
The trajectory of urinary stone disease depends on the stone type, location, and whether obstruction occurs. Bladder stones may cause intermittent signs that wax and wane: periods of blood in urine, straining, and frequent urination interspersed with periods of relative normality. Over time, stones may grow larger, fragment, or multiply, with the clinical significance depending largely on their size and location. The most significant complication occurs when a stone or fragment lodges in the urethra, creating an obstruction that prevents urination. Urethral obstruction is more common in male animals due to their narrower urethral diameter, and a complete obstruction is life-threatening if urine flow is not restored. Signs of uraemia develop rapidly. In cats, published guidance says an untreated obstruction can be fatal within 2 to 3 days, and some sources give as little as 24 to 48 hours. Kidney stones may remain clinically silent for extended periods or may cause progressive kidney damage through chronic obstruction or inflammation.
Signals & patterns
Early signals
Blood-tinged urine
Pink or red discolouration of the urine, or small drops of blood noticed at the end of urination, can be among the earliest signs of bladder stones. The stone's rough surface irritates the bladder lining, causing microhaemorrhage that discolours the urine. The blood may be intermittent, appearing on some days but not others, and may be more noticeable on light-coloured surfaces or litter.
Increased urination frequency
More frequent trips to the litter tray or garden, often producing only small amounts of urine, can indicate bladder irritation from stones. The stone stimulates the sensation of needing to urinate even when the bladder is not full. In cats, owners may notice more frequent visits to the litter tray or small urine patches in the litter rather than the usual larger clumps.
Straining during urination
Visible effort during urination (squatting for longer than usual, vocalising, or adopting an unusual posture) suggests difficulty with urine flow. Small stones or crystals in the urethra can create partial obstruction that makes urination effortful. This sign can be confused with constipation in cats, as the posture for straining to urinate and straining to defecate can appear similar. Straining that produces little or no urine is also how a complete urethral obstruction looks, and a partial blockage cannot be reliably told apart from a complete one at home.
Urinating in unusual locations
Cats may begin urinating outside the litter tray, and dogs may have accidents indoors, as bladder irritation creates discomfort and a pressing need to urinate that overrides normal elimination habits. The animal may associate the litter tray or usual toileting area with pain and seek alternative locations.
Later signals
Inability to urinate
Complete urethral obstruction prevents any urine from passing. The animal makes repeated, increasingly distressed attempts to urinate but produces nothing. The abdomen may become visibly distended as the bladder fills, and the belly may be painful to the touch. This is most common in male cats and is life-threatening: signs of uraemia develop rapidly once urine cannot pass.
Vomiting and lethargy with inability to urinate
When urethral obstruction persists, potassium and waste products accumulate in the blood, producing systemic signs including vomiting, profound lethargy, loss of appetite, and eventually collapse. These signs indicate that the obstruction is already affecting the whole body. Rising blood potassium can slow the heart and disturb its rhythm.
Recurrent urinary tract infections
Some stone types, particularly struvite in dogs, are associated with bacterial urinary tract infections. Recurrent infections despite appropriate treatment may suggest the presence of stones that harbour bacteria within their matrix, creating a persistent nidus of infection that prevents complete resolution.
Click to read about the biological mechanisms
How this is usually investigated
Investigating suspected urinary stones involves confirming the presence and location of stones, identifying the stone type where possible, assessing for concurrent urinary tract infection, and evaluating overall urinary tract health to guide management decisions.
Urinalysis
Diagnostic imaging
Urine culture and sensitivity
Stone analysis
Options & trade-offs
Management of urinary stones involves addressing the presenting clinical signs, removing or dissolving existing stones where appropriate, and implementing strategies to reduce the risk of recurrence. The approach depends on the stone type, location, size, and the animal's overall condition.
Dietary dissolution
Some stone types, particularly struvite stones (especially infection-induced struvite in dogs and sterile struvite in cats), can be dissolved using specially formulated therapeutic diets that alter urine pH and reduce the concentration of stone-forming minerals. Dissolution typically requires feeding the therapeutic diet exclusively for several weeks to months, with periodic imaging to monitor stone size reduction.
Trade-offs: Dietary dissolution avoids the need for surgery or anaesthesia but requires strict dietary compliance and patience, as dissolution may take weeks to months. Not all stone types can be dissolved: calcium oxalate stones require physical removal, while urate and cystine stones in dogs can sometimes be dissolved with a combination of diet and medication. During the dissolution period, monitoring is needed to ensure stones are actually shrinking. Shrinking stones could in theory lodge in the urethra during dissolution, although this has not been reported in the veterinary literature.
Surgical removal (cystotomy)
Surgical opening of the bladder (cystotomy) allows direct removal of all visible stones and provides samples for laboratory analysis. This approach removes the stones at the time of the procedure and is applicable to all stone types and sizes.
Trade-offs: Surgery requires general anaesthesia and a recovery period, with potential complications including surgical site infection, suture line breakdown, and temporary post-operative discomfort. However, it removes the stones in a single procedure and yields stone samples for analysis, which informs prevention planning. Surgery may miss very small stones or crystals that are not visible or palpable during the procedure.
Minimally invasive stone removal
Techniques including voiding urohydropropulsion (flushing small stones out through the urethra), cystoscopy-guided basket retrieval, and laser lithotripsy offer alternatives to traditional surgery for appropriately sized and located stones. These approaches may reduce recovery time compared to surgical cystotomy.
Trade-offs: Minimally invasive options are limited by stone size, number, and the animal's anatomy. They require specialised equipment and expertise that may not be available at all veterinary practices. Very large stones or very numerous stones may still require surgical removal. These techniques still provide stone samples for analysis.
Long-term dietary prevention
Following stone removal or dissolution, therapeutic or modified diets aim to create urinary conditions that discourage recurrence of the specific stone type. This may involve controlling urine pH, reducing dietary concentrations of stone-forming minerals, increasing urine dilution, and addressing any underlying metabolic predispositions.
Trade-offs: Preventive diets require long-term commitment and may need to be fed indefinitely in animals with a strong tendency to form stones. They may be more expensive than standard diets and may not be accepted by all animals. Regular monitoring of urine parameters helps assess the effectiveness of the dietary strategy. No preventive approach guarantees against recurrence, but appropriate dietary management significantly reduces the risk.
Medical management of underlying factors
Treating concurrent urinary tract infections with appropriate antibiotics is needed for infection-induced struvite stones to resolve. For urate stones in dogs, allopurinol can reduce uric acid production. It is a human medicine that is not authorised for animals in the UK and is used under the veterinary medicines cascade, and it can itself lead to xanthine stones, particularly when not combined with a low-purine diet. Maintaining adequate hydration through wet food feeding, water fountains, or other strategies helps dilute urine and reduce mineral saturation.
Trade-offs: Medical management addresses contributing factors but may not remove existing stones. Long-term medication requires regular monitoring for side effects and compliance. Increasing water intake is generally beneficial and low-risk but requires consistent attention to the animal's hydration behaviour. Some medications have specific monitoring requirements.
Common misconceptions
"All urinary stones are the same and can be treated the same way"
Urinary stones vary significantly in their mineral composition, and different stone types require fundamentally different management approaches. Struvite stones may be dissolved with therapeutic diets, while calcium oxalate stones require physical removal. Urate stones in dogs can sometimes be dissolved with a combination of diet and medication. Treating all stones with the same approach can lead to inappropriate management and recurrence. Stone analysis following removal guides prevention.
"Straining in the litter tray always indicates constipation"
The posture cats adopt when straining to urinate can closely resemble straining to defecate, leading many owners to assume their cat is constipated when it is actually experiencing urinary difficulty. This distinction is particularly important because urethral obstruction in male cats is a life-threatening condition that requires rapid intervention, whereas constipation, while uncomfortable, does not usually become dangerous over the same timescale. Whether the cat produces urine, faeces or nothing at all helps distinguish between these possibilities, although this is hard to judge reliably at home.
"Once stones are removed, the problem is solved permanently"
Without appropriate preventive measures, urinary stones have a significant recurrence rate. Calcium oxalate stones in particular have high recurrence rates even with preventive measures. Long-term dietary management, adequate hydration, regular monitoring of urine parameters, and addressing any underlying metabolic or infectious factors are important components of reducing recurrence risk. Understanding that stone management is often a long-term commitment rather than a one-time fix helps set appropriate expectations.
Related conditions
Urinary Tract Infection in Dogs
Urinary tract infections can occur alongside urinary stones, as the stones may irritate the bladder lining and create surfaces where bacteria can establish themselves. In some cases, certain bacteria contribute to the formation of struvite stones by altering urine chemistry.
Urethral Obstruction
Urethral obstruction is a consequence that can occur when a urinary stone lodges in the urethra, preventing the bladder from emptying. This tends to happen more often in male cats and small male dogs, where the urethra is narrower.
Ureteroliths
Ureteroliths are stones that form or become lodged in the ureters rather than the bladder, and they form through the same mechanisms as bladder stones, although the mineral type is not always the same: in cats, most kidney and ureter stones are calcium oxalate. Both conditions reflect the same underlying tendency towards stone formation.
Pyelonephritis
Pyelonephritis can develop when bacteria associated with bladder stones travel upward through the ureters to reach the kidneys. Stones may also form in the kidneys themselves in the context of chronic infection or inflammation.
Hydronephrosis
Hydronephrosis may occur if a stone obstructs the flow of urine from the kidney, causing the kidney's collecting system to swell. This obstruction can happen when a stone forms in or travels to the ureter.
Understanding the type of stone present, through analysis of retrieved stones or through urinary and imaging clues, guides the planning of management and prevention. Encouraging adequate water intake through wet food feeding, providing multiple water sources, or using water fountains can help maintain dilute urine, which is beneficial regardless of stone type. Regular monitoring of urine parameters through periodic urinalysis helps assess whether preventive strategies are maintaining favourable urinary conditions.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS