When to see a vet urgently
Contact a vet immediately if the following signs occur with known or suspected urinary stone disease:
- Your cat vomits, stops eating and becomes clearly lethargic.
- The abdomen or back seems very painful.
- Very little urine or none at all is passed.
- Your cat is unusually weak, cold or has difficulty breathing.
A cat that continues to pass urine may also need urgent help, because obstruction of one kidney does not necessarily stop all urination. You can find a vet near you.
Overview
Kidney stones form from microliths: small crystals that stick together and become compacted over time. Their composition varies, including struvite, calcium oxalate, urate and cystine. Unlike bladder stones, kidney stones often cause no symptoms until they block a ureter or cause renal colic. The condition may be an incidental ultrasound finding, but often presents with sudden pain and urinary problems.
A ureter carries urine from a kidney to the bladder. It is different from the urethra, through which the bladder empties outside the body. A stone moving out of the kidney can become lodged in the ureter and impair drainage from that particular kidney. The other kidney may continue to deliver urine to the bladder.
Many kidney stones in cats consist of calcium oxalate. These cannot be dissolved with diet. The list of compositions therefore does not mean that the different stone types are equally common or treated in the same way. A stone that remains in the kidney without causing harm may instead be monitored under a planned programme.
Causes
- Disturbances of mineral metabolism.
- An unbalanced diet, with too much magnesium, calcium or phosphorus.
- Insufficient drinking.
- Chronic urinary tract infections.
- Hereditary predisposition.
- Hormonal and metabolic disorders, including hypercalcaemia.
Stone formation results from several factors acting together. Urine concentration, acidity and the tendency of minerals to precipitate matter more than the amount of one nutrient considered in isolation. Calcium is an essential nutrient, so do not remove it from the diet yourself. Strong urine acidification intended for struvite may also be the wrong goal for a cat with oxalate stones.
Hypercalcaemia means an elevated blood calcium concentration. Detecting it affects investigations and dietary planning, but not every cat with oxalate stones has hypercalcaemia. A urinary tract infection may accompany stone disease, but finding stones alone does not prove a bacterial infection or a need for antibiotics.
Risk factors
- Cats that eat dry food and drink little.
- Older cats.
- Predisposed breeds, including Persians, Himalayans and Burmese.
- Cats with chronic kidney and urinary tract diseases.
The listed factors do not reliably establish an individual cat's risk. Information on breed-related and hereditary factors in feline kidney stones is limited, and dry food alone does not establish the cause. Young cats can also have stones. Previous stone type, blood calcium and kidney function help guide investigations and prevention.
Typical symptoms
- Blood in the urine (haematuria).
- Pain when urinating.
- Frequent litter tray visits, passing small amounts of urine.
- Renal colic, with severe pain, crying and an arched back.
- Vomiting and refusal to eat.
- Lethargy and dehydration.
- Acute kidney failure if a ureter becomes blocked.
Frequent litter tray visits and painful urination are more typical of bladder or urethral problems than a kidney stone alone. Upper urinary tract obstruction may cause mainly poor appetite, vomiting or withdrawal. A cat may not have an obvious colic episode or an enlarged bladder.
Normal urination or initially fairly normal kidney values do not rule out a one-sided ureteral obstruction. A functioning opposite kidney can mask changes. If your cat's health changes suddenly, even previously stable kidney disease needs reassessment, rather than automatically treating the symptoms as an ordinary worsening of the old condition.
Complications and consequences
- Dilation of the renal pelvis, or hydronephrosis, due to obstruction.
- Chronic kidney failure.
- Pyelonephritis, a secondary bacterial infection of the renal pelvis.
- Kidney rupture in severe obstruction.
- Death without treatment.
Backed-up urine increases pressure within the kidney and can damage functioning tissue. The harm depends on the degree and duration of obstruction. Even a partial blockage is therefore taken seriously. However, not every small kidney stone found by chance means that the kidneys are losing function.
Bacterial infection of the renal pelvis can complicate the situation. However, fever or obvious abdominal pain does not occur in every cat with pyelonephritis. A pus-forming infection trapped behind an obstruction is particularly urgent. Investigation of infection and restoration of urine flow are planned together.
Diagnosis at the vet
- Basic urinalysis for crystals, blood and protein.
- Blood biochemistry to assess kidney function.
- Kidney ultrasound to detect stones and dilation of the renal pelvis.
- X-rays for radiopaque stones, including oxalate and struvite.
- Urine bacterial culture if infection is suspected.
What do the investigations establish?
Investigations aim to distinguish a stone in the kidney, a stone in the ureter and an actual obstruction to urine flow. Crystals alone do not confirm a stone's composition or location. The mineral type of a stone visible on an X-ray is also initially an estimate unless the stone has been recovered for analysis.
Ultrasound assesses both kidneys, the renal pelves and visible portions of the ureters. X-rays can help locate stones and assess their number. If ordinary imaging does not establish the cause of obstruction, more detailed imaging, such as a contrast study or CT scan, is sometimes needed. The method is chosen according to your cat's condition and the findings.
Depending on the situation, blood tests include kidney values, electrolytes and calcium. Urine testing assesses concentration, cells and possible signs of infection. A culture sample is ideally collected before antibiotics, using a method that minimises contamination. Symptoms and results are interpreted together, because one sample cannot describe the entire kidney's function.
Assessing an incidental finding
Your vet compares the finding with earlier images and assesses whether the stone is growing or causing pain, recurrent infection or pressure on kidney tissue. Stones without symptoms are not automatically removed, because the procedure itself can damage the kidney. Monitoring aims to detect changes promptly. Concurrent chronic kidney disease alone does not establish that the stone caused it.
Treatment
When obstruction is suspected, early goals are to stabilise general health, relieve pain and correct dangerous fluid or electrolyte disturbances. Fluid treatment is adjusted to urine production and your cat's condition. Giving large amounts of fluid does not, by itself, remove an impacted stone, and excessive fluids can be harmful.
In selected cases, medical supportive treatment can be tried in hospital while monitoring whether urine flow is restored. This does not mean waiting at home or dissolving a stone with ordinary food. If the condition worsens or the blockage persists, a procedure to restore urine flow is needed. Treatment does not wait for a cat's oxalate stone to dissolve.
Procedures for ureteral obstruction
Depending on the situation, options include a ureteral stent or a subcutaneous bypass system. A stent holds the passage open within the ureter. A subcutaneous ureteral bypass, or SUB, carries urine from the renal pelvis to the bladder around the blocked ureter. Other removal methods may also be considered according to the stone's location.
These procedures require specialist expertise, so your vet may refer your cat for further care. The aim is to preserve usable kidney tissue and restore urine flow. Not every stone in the kidney necessarily needs to, or can, be removed at the same time if ureteral obstruction is the main problem.
Infection, pain and home care
Antibiotics are chosen for a confirmed or strongly suspected infection, using culture and susceptibility results where possible. They are not used for a sterile stone alone. The suitability of pain relief is assessed particularly carefully in a cat with kidney disease. Do not give human painkillers or leftover pet medicines yourself.
After discharge, monitor appetite, drinking, urination and alertness. After a procedure, follow the specific instructions on wound care, protection and movement. Contact the veterinary practice if your cat deteriorates, starts vomiting or stops eating. Symptoms of obstruction can return without an obvious change in the litter tray.
A cat with a stent or bypass system needs planned follow-up. Urine samples and imaging can help identify infection, a new obstruction or a device problem. Do not handle the subcutaneous system yourself; ask the veterinary practice for instructions if anything unusual occurs.
Prognosis
Recovery depends on the initial condition of both kidneys, the duration of obstruction and response to treatment. Blood values may improve when urine flow is restored, but some cats later need treatment for chronic kidney disease. One image or kidney value cannot reliably predict the full extent of recovery. Possible formation of new stones is also considered during follow-up.
Prevention
- Ensure fresh water is available, preferably a drinking fountain to increase drinking.
- Feed a balanced diet.
- Use therapeutic diets if your cat is prone to stones.
- Manage weight and provide exercise.
- Arrange regular urine tests and ultrasound examinations for an at-risk cat.
A fountain suits some cats, but clean water bowls may be equally appealing. Wet food and water added to food can increase fluid intake. The diet is chosen according to stone type and any kidney disease; the same therapeutic food is not automatically suitable for every cat.
Do not add a urine-acidifying product, calcium supplement or stone-prevention medicine without assessment. Elevated blood calcium is investigated and treated separately. Follow-up imaging can detect stone growth or movement before severe symptoms, but the interval between examinations is agreed individually.
Important for cat owners
Nephrolithiasis is a serious disease that can remain hidden until it worsens. Remember that blood in the urine, pain or refusal to eat are warning signs in a cat. Timely diagnosis and dietary adjustments help prevent obstruction and the development of chronic kidney failure.
Dietary changes may reduce recurrence risk, but cannot reliably prevent an existing stone from moving or open an established blockage. Recurrent symptoms therefore need investigation even when the prescribed diet has been followed.
This article provides general information and does not replace veterinary care. Contact a vet if you notice signs of illness in your cat.
Frequently asked questions
Can a cat have a kidney stone while urinating normally?
Yes. A stone in the kidney may cause no symptoms, and with a one-sided ureteral blockage the other kidney can continue to deliver urine to the bladder.
Does every kidney stone need removing?
No. A harmless incidental finding can be monitored. A stone causing obstruction, pain, recurrent infection or tissue damage needs a separate treatment plan.
Can diet dissolve a cat's kidney stone?
Calcium oxalate stones, which are common in cats, do not dissolve with diet. Some other stones can be dissolved in selected situations, but this must not delay treatment of an obstruction.
Does blood in the urine definitely mean a kidney stone?
No. Blood can also come from the bladder or elsewhere in the urinary tract. A urine sample and any necessary imaging help locate the cause.
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
- ACVIM Small Animal Consensus Recommendations on the Treatment and Prevention of Uroliths in Dogs and Cats, Journal of Veterinary Internal Medicine / Utrecht University, accessed 2026-11-03.
- Obstructive Uropathy in Dogs and Cats, Merck Veterinary Manual, accessed 2026-11-03.
- Urolithiasis in Cats, Merck Veterinary Manual, accessed 2026-11-03.
- 2026 iCatCare consensus guidelines on the diagnosis and management of chronic kidney disease in cats, Journal of Feline Medicine and Surgery, accessed 2026-11-03.
- How common are feline kidney stones?, University of Minnesota College of Veterinary Medicine, accessed 2026-11-03.
- Step by step: Risk management for calcium oxalate (CaOx), University of Minnesota College of Veterinary Medicine, accessed 2026-11-03.
- Pyelonephritis in Small Animals, Merck Veterinary Manual, accessed 2026-11-03.
- ISCAID guidelines for the diagnosis and management of bacterial urinary tract infections in dogs and cats, The Veterinary Journal, accessed 2026-11-03.
- Hydration, Cornell Feline Health Centre, accessed 2026-11-03.
- Urinary Stones, American College of Veterinary Surgeons, accessed 2026-11-03.
- Get the Facts about Pain Relievers for Pets, U.S. Food and Drug Administration, accessed 2026-11-03.