Causes of Urine Crystals (Crystalluria) Of Dogs

Several factors can cause the formation of urine crystals in dogs. These include:

• Abnormal urine pH caused by the presence of bacteria
• Abnormal urine pH caused by consumption of poor-quality dog food
• Urine that is too concentrated
• Abnormal concentrations of certain minerals in the urine
• Genetics
• Timing of urine sample collection
• Refrigeration of the urine sample after collection
• Certain medications that can affect concentrations of minerals in the urine

In some cases, urine crystals may only be incidental findings and are not a cause for concern.

Types of Urine Crystals

There are several types of urine crystals in dogs. The most common are:

• Struvite
• Calcium oxalate
• Urates
• Cystine
• Xanthine
• Silica

Struvite and calcium oxalate crystals are the most common in dogs. In addition to these two types of crystals, urate and cystine are also common lower urinary tract stones. These are commonly found in the urinary bladder and urethra of dogs.

Struvite Crystals

Struvite crystals are made up of magnesium, ammonia, and phosphate. More than 50% of struvite crystalluria cases occur in healthy dogs, including those without urinary tract infections. It can be an incidental finding in dogs that are brought in because of other conditions.

Struvite uroliths (stones) in dogs are associated with chronic or recurrent bacterial infection in the urinary tract. There is a higher incidence of struvite urolithiasis in female dogs as a result of a higher prevalence of bacterial urinary tract infections.

Calcium Oxalate

The presence of calcium oxalate crystals is a common finding in healthy dogs. Like struvite crystalluria, a good percentage of dogs with calcium oxalate crystalluria don’t need medical intervention. However, rare cases may be associated with conditions such as hyperparathyroidism, or ingestion of ethylene glycol. These conditions cause increased excretion of calcium in the urine.

Dog breeds that are predisposed to calcium oxalate stones include:

• Bichon Frise
• Maltese
• Miniature Schnauzer
• Lhasa Apso
• Yorkshire
• Pomeranian
• Miniature Poodle
• Shih Tzu

Urate Crystals

There are several types of urate crystals - ammonium urate, uric acid, and sodium urate. The presence of any of these crystals in a dog’s urine may indicate liver disease or congenital defects, causing impaired metabolism of uric acid or increased secretion of uric acid in the urine. Dog breeds with a high risk of abnormal urate crystals include English Bulldogs and Dalmatians.

How Urine Crystals are Diagnosed in Dogs

To check for the presence of crystals, urine samples from your dog will be subjected to urinalysis. Tests will also be performed to check for the urine pH and mineral content. Microscopic examination of urine samples can help identify the type of crystals in your dog’s urine.

If your vet suspects stones (uroliths) may be responsible for your dog’s symptoms, an x-ray or ultrasound may also be performed. If stones are present, imaging can also reveal their size and number.

If there is a bacterial infection, culture and sensitivity testing can help identify the causative agent so an appropriate antibiotic can be given to help dissolve the stone.

Calcium Oxalate Crystals

In dogs with persistent calcium oxalate crystalluria or symptoms of disease, veterinarians usually perform specific tests to assess calcium, blood urea nitrogen (BUN), and creatinine to help rule out other potential causes.

Urate Crystals

Urate urolithiasis should be suspected in dogs exhibiting symptoms of lower urinary tract disease and radiograph-identified uroliths.

Treatment Options for Dogs with Crystalluria

By itself, the presence of crystals in the urine (crystalluria) does not lead to symptoms of lower urinary tract problems. However, intervention should be considered when there is a large number of crystals in the urine of patients with a history of urinary tract obstruction or struvite urolithiasis.

Struvite Crystals

In addition to dietary management, treatment of struvite crystals and prevention of recurrence requires identifying the type of crystal as well as treatment of concurrent bacterial infections of the urinary tract, or prevention of infections.

In some cases where crystals have formed into bladder stones, surgical intervention may be necessary instead of medical dissolution. This is particularly true when your dog is showing severe symptoms or there is obstruction of the urinary tract, and /or pyelonephritis. Other times, struvite stones can be dissolved with a combination of a special diet and medications. The diet is formulated to contain low levels of protein, magnesium, and phosphorus.

Calcium Oxalate Crystals

Medical intervention may be considered in dog breeds that are predisposed to crystal formation and have been observed to have calcium oxalate crystalluria even without stones.

Other indications for intervention include recurrent or persistent infection, symptoms associated with uroliths, obstruction of the urinary tract (partial or total), and if the veterinarian thinks there is a high risk of obstruction. Since urinary stones made of calcium oxalate cannot be dissolved, surgery is needed for removal.

Urate Crystals

If urate crystals are caused by liver dysfunction, the condition should be treated first. Medical therapy may be started, and/or surgical intervention may be performed in patients with urate stones.

How to Prevent Urine Crystals from Recurring

To prevent the recurrence of struvite urolithiasis associated with bacterial infection, measures should be undertaken to prevent urinary tract infections.

Recurrence of urine crystals and stones is usually a result of the following:

• Incomplete dissolution of stones
• Persistence of bacterial infection
• The presence of an underlying problem that affects the normal defense mechanisms of the urinary tract can lead to recurrent infections

Preventing the recurrence of urate crystals and stones involves the correction of underlying disease in dogs with liver dysfunction. Your vet may also recommend a special diet.

Monitoring Your Dog for Urine Crystals

After therapy to dissolve the crystals and/or stones, your dog should be rechecked every 4 weeks or so depending on the recommendation of your vet. During these checkups, urinalysis and urine culture will be performed to confirm if therapy continues to be effective. Radiographs are also taken to monitor the progress of the dissolution. If results show the stone has dissolved, therapy is generally continued for 2-4 weeks.

Read more:

Canine Hormone-Responsive Urinary Incontinence

Diseases of the Dog’s Prostate

Kidney Failure in Dogs

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