What causes crystals in dog urine?

Finding crystals in your dog’s urine can be alarming, but it’s also a useful clue about what’s happening inside. As a veterinarian, I often see owners spot sand-like particles or cloudy urine and worry about stones, infection, or kidney disease. That early observation can shorten the time to useful testing and treatment, so it’s worth knowing what crystals might mean, how urgent the situation is, and what you can do at home right away.

Why finding crystals in your dog’s urine warrants attention

Most people first notice crystals when wiping a dog after urination, finding gritty sediment in a pee pad, or seeing specks or sand in the toilet or grass. I also see crystals discovered on routine urine screening before any symptoms appear, and during workups for frequent licking, accidents in the house, or blood-tinged urine.

Certain groups benefit most from routine urine checks: breeders monitoring young dogs that must remain reproductively and systemically healthy, older dogs with changing bladder habits, and dogs with a history of urinary tract infections or previous bladder stones. Catching crystals early may let your veterinarian intervene before a stone forms that could block the urethra.

Beyond health, crystals can carry emotional and financial weight. A blocked male dog is an emergency that often needs hospitalization and surgery; conversely, catching a crystal pattern early may require only a diet change and monitoring. Awareness helps you prioritize vet visits appropriately and reduces the chance of costly emergency care.

Being attentive won’t prevent every problem, but it makes it more likely that we’ll find the underlying reason sooner—whether that’s a dietary imbalance, infection, or a metabolic condition that requires longer-term management.

Common causes behind crystals in canine urine

Urinary crystals are mineral deposits that form when certain salts become concentrated enough to start solidifying. The most common types seen in dogs are struvite (magnesium-ammonium-phosphate), calcium oxalate, and ammonium biurate (sometimes called urate) crystals. Each tends to appear under different urinary and metabolic circumstances.

Several primary drivers may be involved: very concentrated urine, a urine pH that favors a particular mineral, bacterial infection (especially organisms that split urea), and systemic metabolic conditions such as disorders of calcium metabolism or liver disease. Breed and age can influence risk—young Dalmatians and some breeds with liver shunts are more likely to form urate-type crystals, while small middle-aged neutered dogs often develop calcium oxalate.

How crystals develop in a dog’s urinary tract

At the simplest level, crystals form when urine becomes supersaturated with a mineral. Supersaturation means there is more dissolved material present than the urine can comfortably hold, so particles begin to drop out of solution and serve as seeds for crystal growth. This initial step is called nucleation, and once a tiny particle forms it can grow into a visible crystal or a stone.

Urine pH strongly influences which salts are likely to precipitate. Struvite crystals are more likely when urine is neutral to alkaline, whereas calcium oxalate tends to form in neutral to acidic urine. pH shifts can occur with diet changes, hydration, and bacterial activity.

The kidneys’ handling of minerals matters too. Dogs with higher urinary calcium (hypercalciuria), altered oxalate handling, or metabolic conditions that change how the liver or kidneys process waste products are more likely to shed crystals. For example, ammonium urate crystals are often linked to abnormalities in the liver’s ability to process uric acid or congenital portosystemic shunts.

Certain bacteria produce the enzyme urease, which splits urea into ammonia and raises urine pH. This increase in pH makes struvite formation more likely, so a urinary tract infection with a urease-producing organism is a common pathway to struvite crystals and stones.

When crystals are most likely to form: risk factors and life stages

Dehydration and chronically concentrated urine are among the simplest and most common contributors. Dogs that drink little, live in warm climates without available water, or eat only dry food may pass more concentrated urine and therefore have more opportunity for crystals to form.

Diet composition matters. Diets high in certain minerals, or that tend to make urine more alkaline or more acidic, can shift the balance. High-purine diets may increase certain waste products, while therapeutic diets exist that intentionally alter urine pH and mineral content to reduce risk of specific stone types.

The presence and timing of urinary tract infections is important. A urine sample taken after antibiotics or improperly stored may give misleading results—bacteria can die and crystals can dissolve or form in the sample post-collection. Some medications and systemic diseases (for example, conditions that alter calcium or liver function) may predispose a dog to particular crystals.

Finally, sample handling can be a culprit. If urine is left at room temperature for hours, bacteria can multiply and change the pH, producing crystals that weren’t present in the bladder. Always aim to get a fresh sample to the clinic quickly or refrigerate if you must delay.

Warning signs: red flags that need urgent veterinary attention

Not all crystals are emergencies, but specific signs require immediate veterinary attention. Straining to urinate, repeated trips to the litter area with little or no urine produced, and sudden collapse are classic signs of urinary obstruction—especially in male dogs, whose narrower urethra makes them more prone to blockages. This is an emergency.

Painful urination, frequent licking of the genital area, visible blood in the urine, fever, or a sudden change in behavior or appetite also warrant prompt evaluation. These symptoms may suggest infection, inflammation, or the beginning of a stone-related problem.

On laboratory testing, findings that are concerning include elevated kidney values (BUN, creatinine), which may suggest reduced kidney function, or severe electrolyte imbalances. If bloodwork shows signs of systemic infection or significant dehydration, that increases the urgency. Recurrent infections or persistent abnormal urine sediment despite treatment should prompt referral or imaging to look for stones and underlying causes.

What to do immediately if you suspect crystals in your dog’s urine

If you find crystals, collect a fresh urine sample if you can. I typically recommend midstream collection in a clean, wide-mouth sterile container; for small dogs you can catch urine with a shallow cup or use a commercially available collection kit. Try to get the sample to your veterinarian within two hours; if you must delay, refrigerate the sample and bring it in within 12–24 hours.

When you call the clinic, be ready to tell the veterinarian the dog’s diet (brand and type), recent water intake and changes, any vomiting or diarrhea, medications or supplements given in the last month, prior history of stones or infections, and how long you’ve noticed the current changes. Photos of the urine sediment or video of urination can be helpful.

Short-term supportive steps at home include increasing access to water—offer fresh bowls in multiple locations, and consider wet food temporarily—but avoid starting over-the-counter medications or urinary acidifiers without veterinary guidance. If your dog shows signs of obstruction (straining without passing urine, repeated unsuccessful attempts, severe pain, collapse), go to an emergency clinic immediately.

Practical at-home prevention: diet, hydration and routine tips

One of the most practical long-term strategies is simply promoting good hydration. Switching some or all of a dog’s food to canned or mixing water into kibble can dilute urine and reduce the tendency to form crystals. Many dogs drink more when offered moving water from a fountain or when bowls are placed in several locations.

Work with your veterinarian to choose a diet that targets the specific crystal type if your dog has a known tendency. Therapeutic diets are formulated to change urine pH and mineral content safely; they should be used under guidance, because over-correction can create new problems. Consistency is also important—sudden frequent diet changes may be counterproductive.

Monitor frequency, color, and odor of urine and keep a simple log if you’re tracking a recurrent issue. Note episodes of visible sediment, blood, or difficulty urinating. Simple hygiene—regularly cleaning bedding, grooming the belly and genital area, and changing outdoor or indoor elimination spots—can reduce bacterial contamination that might lead to infection and struvite crystal formation.

Useful tools and products for monitoring and managing urinary health

• Sterile urine collection containers or commercial urine collection kits designed for dogs—these make a cleaner sample and are often sold through your clinic or online.
• Urine dipsticks or pH test strips (veterinary grade recommended); pH strips give a quick sense of acid vs alkaline urine, but they don’t replace microscopic sediment exam or culture.
• Pet water fountains, extra shallow bowls, and food measuring tools to encourage drinking and maintain consistent feeding amounts.
• Measuring cups or a small kitchen scale to portion therapeutic diets accurately, and a notebook or app to record urine changes and episodes.

Sources and further veterinary reading

• Merck Veterinary Manual: “Urolithiasis in Dogs and Cats” — section on urinary crystals and stone management.
• ACVIM Consensus Statement: Diagnosis and Management of Bacterial Urinary Tract Infections in Dogs and Cats (2020 update) — guidance on culture, treatment, and when to investigate underlying disease.
• Nelson, R. W. and Couto, C. G., Small Animal Internal Medicine, 6th Edition — chapters on urinary tract disease and urolithiasis.
• Lulich, J. P., Osborne, C. A., “Urolithiasis in Dogs and Cats,” Veterinary Clinics of North America: Small Animal Practice — review of stone types, epidemiology, and prevention strategies.