When to see a vet urgently
Contact a vet immediately if your cat has any of the following:
- repeated straining with no urine or only drops;
- severe pain, crying or restlessness during attempts to urinate;
- urinary signs accompanied by vomiting, failure to eat or marked tiredness;
- sudden weakness or collapse.
Severe urinary problems need investigation in female cats too. Find a vet near you.
Overview
Calcium oxalate forms in urine when calcium and oxalic acid concentrations are high and conditions are unfavourable, such as low pH or a lack of protective factors. The stones are hard and dense and cannot be dissolved with diet or medicines, unlike struvite stones.
In cats, the disease often causes recurrent bladder inflammation, painful urination and repeated urethral obstructions.
Stone location affects the consequences. A ureter carries urine from a kidney to the bladder, while the urethra carries it out. Obstruction at these sites creates different situations requiring different procedures. Calcium oxalate stones can also occur in a kidney without obvious difficulty urinating.
Stone formation is encouraged by supersaturated urine, containing more dissolved minerals than it can keep in solution. Urine concentration, calcium excretion and acidity act together. One low pH result therefore cannot explain stone formation alone.
Causes
- mineral metabolism disorders, such as excessive calcium excretion in urine or high blood calcium;
- an inherited predisposition;
- an unbalanced diet containing excessive calcium or vitamin D;
- little drinking and concentrated urine;
- chronic diseases, such as tumour-associated hypercalcaemia, hyperparathyroidism and chronic kidney disease;
- older age, with risk increasing from 7–8 years.
Raised blood calcium is not always caused by a tumour or parathyroid disease. Cats can also have idiopathic hypercalcaemia, where the cause remains unknown after investigation. Conversely, not every cat with oxalate stones has high blood calcium.
The age mentioned is not a lower limit for the disease. Risk is assessed through the whole situation, and younger cats with symptoms are investigated too. Age and feeding pattern alone cannot confirm or rule it out.
Risk factors
- middle-aged and older neutered males;
- inactivity and obesity;
- poor-quality dry food without adequate drinking;
- chronic urinary tract infections;
- breed predisposition, for example in Persians, Birmans and Himalayans.
Dry food alone does not establish the cause. Dietary effects are assessed through composition, water intake and urine characteristics. Breed-associated findings vary between studies, and not every predisposition listed has equally strong evidence.
Calcium oxalate stones do not usually form because of bacterial infection. Bladder irritation can cause inflammatory symptoms without bacteria. A concurrent infection is possible, but is investigated separately rather than automatically inferred from stones or blood in the urine.
Typical symptoms
- frequent, painful attempts to urinate;
- blood in the urine, known as haematuria;
- vocalising during urination;
- genital licking;
- incontinence or passing drops;
- complete failure to pass urine when the urethra is blocked, an emergency;
- lethargy, loss of appetite and vomiting with complications.
A stone may irritate the bladder without initially causing clear signs and be found during another investigation. In another cat, even a small stone may enter the urethra and become lodged. A larger stone may intermittently interfere with bladder emptying.
Urinating outside the litter tray may indicate pain. Repeated visits or straining should not be regarded solely as a behavioural problem or constipation. A few drops do not demonstrate normal bladder emptying.
Complications and consequences
- acute urinary retention, life-threatening in males;
- enlargement of the renal pelvis and kidney damage;
- chronic bladder inflammation;
- repeated urinary tract obstructions;
- chronic kidney failure.
A stone in a kidney or ureter may obstruct urine outflow and cause acute kidney injury. This differs from lower urinary tract obstruction. A kidney stone's significance is assessed through obstruction, pain, infection and its effect on kidney tissue.
Stones can recur after removal because the procedure does not itself change urine composition. Prevention and monitoring are therefore part of care even when urination quickly returns to normal.
Diagnosis at the vet
- routine urine testing for calcium oxalate crystals, blood and inflammatory cells;
- bladder and kidney ultrasound;
- X-rays, as oxalate stones are radiopaque and show clearly;
- blood biochemistry to assess calcium and kidney values;
- investigation of associated conditions, such as hormonal disorders.
Urinary crystals alone do not confirm stone composition. Crystals may occur without stones, and a stone may be present without detectable crystals. Cooling and delays in examining a sample can also alter findings. Urine pH and crystal type are therefore assessed alongside imaging and other tests.
X-rays and ultrasound help establish stone number, size and location and any consequences of obstruction. Small stones may require careful imaging, and a clear urine sample does not rule them out. A removed stone is sent for composition analysis so prevention is based on the confirmed mineral rather than appearance alone.
Blood tests assess kidney function, total calcium and, where needed, ionised calcium, the biologically active form. Further investigation of abnormal calcium depends on the findings. If bacterial infection is suspected, urine culture helps select an antibiotic. Culture results are also interpreted alongside symptoms.
Treatment
- acute obstruction: immediate catheterisation, bladder flushing and stabilisation;
- stone removal: surgery, called cystotomy, or endoscopic techniques;
- diet: special foods reducing new stone risk, without dissolving existing stones;
- supportive care: pain relief and anti-inflammatory medicines;
- treatment of an underlying disease, such as hypercalcaemia.
For urethral obstruction, urine flow is restored while systemic problems are treated. Catheterisation does not mean oxalate stones remaining in the bladder have been removed. Size, location and the cat's anatomy determine whether endoscopy or another less invasive method is possible, or surgery is needed.
A ureteral obstruction is not usually resolved by the same catheterisation through the bladder used for a urethral blockage. Treatment is planned separately according to kidney function and imaging. Conversely, symptom-free kidney stones are not all removed automatically if they cause no clinically important harm. Monitoring needs are still assessed.
Pain relief is matched to hydration, kidney function and other medicines. Antibiotics are not prescribed simply because a bladder stone is present. Treating hypercalcaemia and feeding to prevent recurrence have different goals from removing an existing stone.
Home care and monitoring
Monitor actual urine output, straining, visible blood, appetite and energy. Recurring symptoms warrant contact even if a previous stone was removed. Failure to urinate or clear difficulty is urgent even soon after discharge.
After surgery, restrict movement as instructed, keep the wound dry and prevent licking. Do not apply your own cleansers. Increasing swelling, discharge, wound opening or bleeding requires assessment. External wound healing does not replace monitoring urinary signs.
Follow-up may assess urine concentration and pH and repeat urinary tract imaging. Imaging can reveal new stones before symptoms. The interval depends on previous findings, location, recurrence and other diseases; the same schedule does not apply to every cat.
Prognosis
The outlook depends on obstruction location and duration, the degree of kidney damage and other diseases. Removal can relieve symptoms, but recurrence risk remains. A kidney patient's diet and medicines must also help preserve kidney function, so plans are individual.
Prevention
- Encourage adequate drinking with options such as fountains and wet food.
- Use good-quality food with balanced minerals.
- Maintain a normal body weight and prevent obesity.
- Arrange regular examinations and urine tests for cats over 7 years.
- Reduce stress affecting urination.
The diet aims to reduce new stone formation, rather than dissolve oxalate. A strongly acidifying diet intended to dissolve struvite should not be transferred unchanged to an oxalate patient. Do not give acidifying or alkalinising supplements yourself either. The vet may consider medication alongside diet where needed.
Wet food or adding water to food can dilute urine. Offer fresh water in accessible places and prevent competition between animals at drinking sites. Not every cat likes a fountain, so provide bowls according to preferences too. Treats and any supplements are included in the feeding plan.
Progress towards goals is assessed with tests, rather than simply judging drinking by eye. Seven years is not the sole basis for monitoring: a younger cat with previous stones or symptoms may also need follow-up.
Important for cat owners
Calcium oxalate stone disease is a common, dangerous urinary condition in cats. Remember that severe or painful urination in a male cat is an emergency needing an immediate veterinary visit. Timely diagnosis and appropriate treatment prevent serious complications and protect health.
This article provides general information and does not replace veterinary care. If your cat cannot urinate, contact a vet or emergency practice immediately.
Frequently asked questions
Can calcium oxalate stones be dissolved with special food?
No. Feeding helps reduce new stone formation, but treatment of an existing stone depends on location, symptoms and obstruction risk.
Do oxalate crystals always mean urinary stones?
No. Crystals and stones can occur separately, and sample handling also affects crystals. Identifying a stone usually requires imaging, while confirming a removed stone's type requires composition analysis.
Can stones return after successful surgery?
Yes. Surgery does not remove every factor underlying formation. Preventive feeding, water intake, treatment of any hypercalcaemia and agreed checks continue after recovery.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
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- Step by step: Risk management for calcium oxalate (CaOx), University of Minnesota College of Veterinary Medicine, accessed 2026-11-03.
- How common are feline kidney stones?, University of Minnesota College of Veterinary Medicine, accessed 2026-11-03.
- Urinalysis, Merck Veterinary Manual, accessed 2026-11-03.
- Blocked bladder in cats, PDSA, accessed 2026-11-03.
- Calcium Oxalate Bladder Stones in Cats, VCA Animal Hospitals, accessed 2026-11-03.
- Hydration, Cornell Feline Health Centre, accessed 2026-11-03.
- Diagnostic testing, AAHA, accessed 2026-11-03.
- Care of Surgical Incisions in Cats, VCA Animal Hospitals, accessed 2026-11-03.