Urolithiasis

TL;DR. Urolithiasis is a common condition where mineral stones form in the urinary tract of dogs and cats, causing pain, bloody urine, and potentially life-threatening blockages.

Urolithiasis can affect both dogs and cats, causing stones to form anywhere in the urinary tract.

What is it?

The urinary system of dogs and cats is designed to filter waste products from the blood and excrete them as liquid urine. This system consists of the kidneys, the ureters (thin tubes connecting the kidneys to the bladder), the urinary bladder (a muscular storage pouch), and the urethra (the tube through which urine exits the body).

Urolithiasis is a common metabolic and urinary disorder characterized by the formation of solid mineral stones, known scientifically as uroliths or urinary calculi, within this tract. Depending on where these stones develop, the condition may be referred to as nephrolithiasis (kidney stones), ureterolithiasis (ureteral stones), or cystolithiasis (bladder stones).

As a leading veterinary internal medicine reference explains:

"Urolithiasis is a common urinary tract disorder of dogs and cats. Clinical signs of urolithiasis are variable, depending on the location of the urolith. Pollakiuria, stranguria, dysuria, and hematuria may be noted by owners and suggest a problem in the lower urinary tract."

These stones begin as microscopic crystals suspended in the urine. When the urine becomes oversaturated with minerals, these crystals precipitate out of solution and begin to clump together. If they are not flushed out during normal urination, they gradually grow into solid, rock-like structures. These stones cause severe irritation, bleeding, and inflammation of the delicate lining of the urinary tract. Most critically, they can physically block the flow of urine, creating a life-threatening medical emergency.

Causes & risk factors

The formation of urinary stones is a complex process influenced by a combination of genetics, diet, lifestyle, and metabolic factors. Different types of stones form under different chemical conditions within the urine. The most common mineral compositions found in pets are calcium oxalate, struvite (magnesium ammonium phosphate), and urate.

In recent decades, veterinarians have noted a significant shift in the types of stones most frequently diagnosed in dogs. According to veterinary internal medicine literature:

"The reasons for the increase in submissions of CaOx from dogs are likely multifactorial and could include demographic and nutritional changes that occurred during this period. Some factors might include feeding a more acidified diet, changes in mineral content of the diets, increase in canine obesity, and possibly a trend favoring ownership of breeds that are more prone to CaOx urolith formation."

Dietary formulation plays a major role in stone formation. Diets that excessively alter urine pH or contain high concentrations of minerals like calcium, phosphorus, oxalate, or magnesium can trigger crystal precipitation. For example, highly acidic urine promotes the formation of calcium oxalate stones, whereas highly alkaline urine encourages struvite stones.

In cats, a unique form of non-crystalline stone can also occur, known as dried solidified blood (DSB) calculi. As described in veterinary textbooks:

"stones, none of them was ever comprised of 100% DSB, as in cats. DSB calculi can occur in various places in the upper and lower urinary tract. DSB calculi are very firm and 'stonelike' but usually do not contain crystalline material... They are generally radiolucent unless they contain a significant portion of" other minerals.

Other risk factors include chronic urinary tract infections (which can alter urine pH and provide a nucleus for stone growth), low water intake, infrequent urination, and obesity.

Signs to watch for

The symptoms of urolithiasis vary depending on the location of the stones and whether they are causing a partial or complete obstruction of urine flow.

Common Lower Urinary Tract Signs:

• Stranguria: Straining to urinate, where your pet may spend a long time in a urinating posture with little to no urine produced.
• Hematuria: Blood in the urine, which may appear pink, red, or contain small clots.
• Pollakiuria: Abnormally frequent urination, often resulting in only a few drops at a time.
• Dysuria: Painful urination, which may cause your pet to whimper, cry out, or show visible distress while urinating.
• Straining to urinate: Owners frequently mistake this behavior for difficulty defecating (constipation).

Occasional or Systemic Signs:

• Inappropriate urination: Urinating in unusual locations, such as on carpets, furniture, or next to the litter box.
• Frequent licking of the genital area: Driven by local pain and irritation.
• Abdominal or lumbar pain: Your pet may hunch their back, tense their abdominal muscles, or resist being handled around the belly or lower back.
• Distended bladder: A large, firm, painful bladder that can be felt during a physical examination.
• Lethargy and Anorexia: Loss of energy and refusal to eat, which are common when systemic illness or severe pain develops.
• Vomiting: A critical sign that often indicates a complete urinary blockage, leading to a buildup of toxic waste products in the bloodstream.
• Polydipsia and Polyuria: Increased drinking and increased urine volume, occasionally associated with upper urinary tract stones.
• Weight loss: Seen in chronic cases, particularly those affecting the kidneys.
• Hyperkalemia and Metabolic acidosis: Life-threatening electrolyte and acid-base imbalances that occur when a pet is completely unable to excrete waste products due to a blockage.

Straining to urinate is a primary sign of lower urinary tract distress and potential blockage.

How vets diagnose it

Diagnosing urolithiasis requires a systematic veterinary evaluation to locate the stones, identify their mineral composition, and assess your pet's overall health.

Your vet will begin with a physical examination, including gentle palpation of the abdomen. In cases of lower urinary tract obstruction, the vet can often feel a large, firm, tense bladder that the pet cannot empty. In cats, this presentation is classic for feline urologic syndrome (FUS). As veterinary surgical texts state:

"The diagnosis of FUS is based on history, clinical signs, and palpation of a large, firm, tense bladder. The history may include urination in unusual locations along with increased frequency in attempts to urinate. This increased frequency may be mistaken for tenesmus by the client."

To confirm the diagnosis and locate the stones, your vet will recommend several diagnostic tests:

• Plain Radiography (X-rays): Many common stones, such as calcium oxalate and struvite, are radiopaque (visible on standard X-rays). However, some stones, such as urate or dried solidified blood (DSB) calculi in cats, are radiolucent (invisible on standard X-rays).
• Contrast Cystourethrograms: This specialized X-ray technique involves injecting a contrast dye into the urinary tract to outline and reveal radiolucent stones.
• Abdominal Ultrasonography: An excellent, non-invasive tool that allows the vet to visualize the inside of the bladder and kidneys. Ultrasound can detect both radiopaque and radiolucent stones, as well as assess bladder wall thickness.
• Serum Biochemical Profile: This blood test checks kidney function (BUN and creatinine) and monitors for dangerous electrolyte shifts, such as elevated potassium (hyperkalemia) and metabolic acidosis.
• Urine Culture and Stone/Bladder Mucosa Culture: These tests identify concurrent bacterial urinary tract infections, which must be treated alongside the stones.
• Crystallographic Analysis: This is the gold standard for diagnosis. Once a stone is retrieved (either surgically or passed naturally), it must be sent to a specialized laboratory to determine its exact mineral composition. This is the only way to formulate an effective long-term prevention plan.
• DNA Testing: Available for certain breeds to identify genetic mutations that predispose them to specific stone types.

Abdominal ultrasound is a highly effective tool for visualizing both radiopaque and radiolucent stones.

Treatment options

Treatment strategies depend on whether your pet is experiencing a life-threatening urinary blockage, the suspected mineral type of the stones, and their location within the urinary tract.

Emergency Stabilization
If a pet is completely blocked and cannot urinate, immediate emergency intervention is required. As veterinary surgical literature emphasizes:

"This situation requires emergency treatment to remove the urethral obstruction and reestablish urine flow."

Your vet will place a urinary catheter under sedation or anesthesia to flush the blocking stone back into the bladder or bypass the obstruction. Intravenous fluids will be administered to flush the kidneys, correct metabolic acidosis, and lower dangerous potassium levels.

Medical Dissolution and Management
Some types of stones, such as struvite, can be dissolved medically using specialized therapeutic diets. These diets restrict specific minerals and adjust urine pH to dissolve the stones back into the urine.

• Urinary Alkalinizers: Medications such as potassium citrate may be prescribed to increase urine pH (making it more alkaline), which helps prevent and manage certain stone types like calcium oxalate and urate.
• Xanthine Oxidase Inhibitors: Allopurinol is a medication used to reduce the production of uric acid. It is commonly prescribed for breeds prone to urate stones, such as Dalmatians, to prevent stone formation or assist in dissolution.
• Supportive Care and Parenteral Agents: In complex metabolic cases or patients requiring intensive nutritional support, your vet may utilize advanced therapies. For example, Intravenous Fat Emulsion may be incorporated into parenteral nutrition plans or used as an antidote for specific lipid-soluble toxicities if systemic complications arise.

Surgical and Minimally Invasive Removal
Stones that cannot be dissolved medically (such as calcium oxalate) must be physically removed. This can be achieved through a cystotomy (a surgical procedure to open the bladder and retrieve the stones) or minimally invasive techniques like laser lithotripsy (using lasers to break up stones) or voiding urohydropropulsion (flushing small stones out of the bladder).

Prognosis

The prognosis for pets with urolithiasis is highly variable and depends on the location of the stones, the stone type, and how quickly treatment is initiated.

For lower urinary tract stones (bladder stones) that are successfully removed or dissolved, the short-term prognosis is excellent. However, urolithiasis is a chronic, recurring disease. Without strict lifelong dietary and lifestyle management, many pets will form stones again.

The prognosis is significantly more guarded for upper urinary tract stones (those in the kidneys or ureters), particularly in cats. Medical management of ureteral obstruction in cats has a 12-month survival rate of 66%. Unfortunately, approximately 32% of cats fail to respond to medical therapy and die or are euthanized within 1 month of diagnosis. This highlights the critical importance of early detection and close veterinary monitoring.

Prevention

While not all cases of urolithiasis can be entirely prevented, the risk of recurrence can be dramatically reduced through targeted strategies:

• Dietary Compliance: Feeding a veterinary-prescribed therapeutic diet is the single most effective way to prevent stone recurrence. These diets must be fed exclusively; giving treats or table scraps can alter urine chemistry and trigger stone formation.
• Increased Water Intake: Keeping urine dilute is crucial. Encourage your pet to drink by providing fresh water, using pet water fountains, or feeding canned food instead of dry kibble. Dilute urine keeps mineral concentrations low and encourages frequent urination, flushing out crystals before they can bind together.
• Regular Monitoring: Routine urinalysis, urine cultures, and veterinary check-ups allow for early detection of crystals or silent infections before they develop into full-sized stones.
• Genetic Screening: For breeds with known genetic predispositions, DNA testing can help breeders make informed decisions and allow owners to start preventative measures early in life.

When to call your vet

You should contact your veterinarian if you notice any changes in your pet's urination habits, such as minor straining, blood in the urine, or urinating in unusual places.

You must seek emergency veterinary care immediately if your pet exhibits any of the following signs of a urinary blockage:

• Straining repeatedly with little or no urine produced
• Crying out or whimpering while attempting to urinate
• Vomiting or extreme lethargy
• A hard, swollen, or painful abdomen
• Frequent licking of the genital area combined with an inability to urinate

For specific breeds

Certain breeds carry a significantly higher risk of developing specific types of urinary stones due to genetic mutations or anatomical factors.

Dalmatians
Dalmatians have a unique, inherited defect in how they metabolize purines. A leading veterinary textbook explains:

"All Dalmatians excrete relatively high amounts of uric acid (400-600 mg of uric acid/day as compared with 10-60 mg/ day in non–Dalmatian dogs); however, not all Dalmatians form urate uroliths. Genetic studies have reported that the mode of inheritance is not X-linked..."

Because of this high uric acid excretion, Dalmatians are highly predisposed to forming ammonium urate stones. They require specialized low-purine diets and close monitoring of their urine pH.

Cavalier King Charles Spaniel
This breed is predisposed to specific metabolic stone types, with research indicating an autosomal recessive mode of inheritance. Genetic testing can help identify at-risk individuals.

Other At-Risk Breeds

• Dogs: Newfoundland (known genetic risk), Black Russian Terrier, [English Bulldog](/p/breeds/englishbulldog_dog), Keeshond, Maltese, Miniature Schnauzer, Pomeranian, Bichon Frise, Cairn Terrier, and Dachshund.
• Cats: Persian, Siamese, Himalayan, and Egyptian Mau.

Sources

• Current Techniques in Small Animal Surgery, 5th Edition, page 515.
• Small Animal Internal Medicine, 5th Edition, pages 721, 723, 728, 731.

My highlights & notes

New note