CONDITION

Urinary Stones (Urolithiasis)

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 are a common component of feline lower urinary tract disease (FLUTD), which typically presents in young to middle-aged 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 represents a situation that can progress from discomfort to life-threatening metabolic crisis within hours if urine flow is not restored. 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 box 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 box 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.

Urinating in unusual locations

Cats may begin urinating outside the litter box, and dogs may have accidents indoors, as bladder irritation creates urgency and discomfort that overrides normal elimination habits. The animal may associate the litter box 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 pressing on the belly may cause pain. This is most common in male cats and represents a situation where metabolic consequences can develop rapidly.

Vomiting and lethargy with inability to urinate

When urethral obstruction persists, potassium and other 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 has progressed to produce metabolic derangement.

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

Purpose: Analysis of a urine sample provides information about urine concentration, pH, the presence of blood, protein, bacteria, and crystal type. The pH and crystal type found in the urine can provide preliminary clues about the likely stone composition, though urine crystals do not always correlate with the stone type present. The presence of bacteria and white blood cells suggests concurrent urinary tract infection.
Considerations: Fresh urine samples provide the most accurate results, as crystals can form or dissolve in stored samples. The method of collection (free-catch, cystocentesis, or catheterisation) may influence the findings. Crystals in the urine indicate supersaturation with certain minerals but do not confirm the presence of stones, just as the absence of crystals does not exclude stones.

Diagnostic imaging

Purpose: Abdominal radiographs (X-rays) can detect most bladder and kidney stones, as many stone types are radiopaque (visible on X-ray). Abdominal ultrasound provides complementary information and can detect radiolucent stones that may not appear on radiographs. Ultrasound can also assess bladder wall thickness, kidney architecture, and the presence of ureteral stones.
Considerations: Some stone types, particularly urate and cystine stones, may be poorly visible or invisible on radiographs and require ultrasound or contrast studies for detection. The size, number, and location of stones on imaging helps guide management decisions. Ureteral stones may require specialised imaging for definitive identification.

Urine culture and sensitivity

Purpose: Bacterial culture of urine identifies whether infection is present and which antibiotics the bacteria are sensitive to. This is particularly important for struvite stones in dogs, where infection-induced stones require treatment of both the stones and the underlying infection for resolution.
Considerations: Culture results take several days to return and require an aseptically collected sample (ideally cystocentesis) for accuracy. Identifying the specific bacterial species helps determine whether the organism is urease-producing, which directly influences whether infection could be driving struvite stone formation.

Stone analysis

Purpose: Quantitative analysis of retrieved stones determines their mineral composition, which is essential for planning prevention strategies. Stone composition cannot be definitively determined by imaging alone, and the same urinary signs can be produced by different stone types that require different management approaches.
Considerations: Stone analysis requires a physical sample, either from surgical removal, voided stones caught during urination, or stones retrieved by other techniques. The analysis reveals whether the stone is composed of a single mineral or is a compound stone with layers of different minerals. Understanding the stone type directly influences dietary and medical prevention strategies.

Options & trade-offs

Management of urinary stones involves addressing the immediate 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, urate, and cystine stones generally require physical removal. During the dissolution period, monitoring is needed to ensure stones are actually shrinking. There is a risk of urethral obstruction if fragmenting stones become lodged during dissolution.

Surgical removal (cystotomy)

Surgical opening of the bladder (cystotomy) allows direct removal of all visible stones and provides samples for laboratory analysis. This is the most definitive approach for immediate stone removal 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 provides immediate resolution and yields stone samples for analysis, which is essential for planning prevention. 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 essential for infection-induced struvite stones. For urate stones, medications such as allopurinol can reduce uric acid production. 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

Misconception:

"All urinary stones are the same and can be treated the same way"

Reality:

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 may respond to medication. Treating all stones with the same approach can lead to inappropriate management and recurrence. Stone analysis following removal is essential for guiding prevention.

Misconception:

"Straining in the litter box always indicates constipation"

Reality:

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 potentially life-threatening condition that requires rapid intervention, whereas constipation, while uncomfortable, generally carries less immediate risk. Observing whether the cat produces urine or faeces — or nothing at all — helps distinguish between these possibilities.

Misconception:

"Once stones are removed, the problem is solved permanently"

Reality:

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.

Understanding the type of stone present — through analysis of retrieved stones or through urinary and imaging clues — is fundamental to planning effective 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: 24 April 2026 · Dr Alastair Greenway MRCVS