Canine Kidney Stones

What are urine crystals?

Urine crystals are the microscopic formation of certain minerals into solids within the urine. This condition is called crystalluria.

Anytime a dog eats or drinks, nutrients are absorbed and waste products need to be eliminated. Some waste products are broken down and eliminated through feces, while others are eliminated in urine. Urine is made by the kidneys filtering the blood and removing salts, waste products and water. These components make up urine.

The urine passes from the kidneys through tiny tubes called ureters to the bladder. It is stored in the bladder until it is time to urinate. The urine then travels out another tube called the urethra and leaves the body.

Normal urine is a balance of water, minerals, acids and protein-breakdown products such as urea. This balance is important. If there is too much of a particular mineral, it will precipitate out into a solid and form crystals.

Urine pH can be acidic (low) or alkaline (basic, or high), depending on many factors, including diet, filtered waste and infection. The pH can affect the contents and concentration of the urine. Sometimes urine will contain other elements, such as crystals; pus, which is white blood cells; bacteria; urinary-tract cells; sperm in male dogs, or red blood cells.

How do urinary crystals form?

If you can remember back to your high school chemistry class, you will recall that crystals will form in solutions when there is an overabundance of certain molecules — for example, the salt crusting on a bucket of ocean water after the water has evaporated.

In some cases, crystals in the urine may be a minor finding and cause no trouble. Examples of normal crystalluria are when the urine is highly concentrated, as opposed to clear and very dilute, or if the urine sample is not fresh. Temperature, diet and urine pH can also affect crystal formation in the urine.

Sometimes enough urine crystals form that they clump together and form a sand-like sediment. This sediment can make urination very uncomfortable. The clumps can continue to accumulate until actual stones form in the bladder. They look like pebbles inside the urinary bladder.

As long as your dog is able to urinate and has a good stream of urine, crystals can be addressed over time, often with nutritional management. If at any time your dog is straining and unable to urinate, there may be a blockage of the urethra, preventing him from passing urine. This is a medical emergency. Untreated urinary blockages can lead to kidney failure and death within a matter of hours.

What do crystals in dog urine look like?

Crystals in urine are not visible to the naked eye. They can only be seen under a microscope. There are many different types of crystals. Some look like clear, square or rectangular gemstones, while others look more like crystal fireworks or hexagons.

If the dog has enough crystals to make a sand-like sediment, the grit may be seen in the urine. These clumps of crystals look like grains of sand.

Are there different types of crystals?

Struvite crystals are composed of magnesium ammonium phosphate. Low numbers of struvite crystals are considered normal for some dogs. They occur most commonly in alkaline (pH higher than 7) urine or urine that is not fresh. Struvite crystals can also be associated with infection, which is one of the things your veterinarian will test for if she finds crystals in your dog’s urine. The presence of large numbers of struvite crystals can lead to bladder stones in dogs.

Struvite crystals are seen more often in younger female dogs. Labrador Retrievers, Cocker Spaniels, Shih Tzus and Bichon Frises are especially prone to developing these crystals.

Calcium oxalate crystals are one of the most common type of crystal found in canine urine. Dogs excreting high amounts of calcium or oxalic acid in their urine can form these crystals. They can also be found in normal urine, especially if the urine is acidic (pH lower than 7) or if the urine has been refrigerated. These crystals can also indicate the presence of a urinary-tract infection and lead to the development of calcium-oxalate bladder stones.

Certain breeds are more genetically predisposed to forming this type of crystal. These include Pomeranians, Miniature Schnauzers, Bichon Frises, Maltese, Yorkshire Terriers, Lhasa Apsos and Miniature Poodles.

Ammonium urate crystals, when found in large quantity in canine urine, may be a sign of liver disease or a genetic mutation. The Bulldog and Dalmatian are predisposed to developing this type of crystal. Miniature Schnauzers, West Highland White Terriers, Yorkshire Terriers and Pekingese are more likely to get these crystals due to liver shunts.

Cystine crystals are a rare type of urine crystal that are radiolucent, meaning they do not show up on X-rays. These crystals develop in dogs that have an inherited issue with their kidneys so that they are unable to reabsorb the cysteine amino acid in the normal fashion. Cystine crystals form into small, circular grey-green stones that can become wedged in the urethra of male dogs and cause a life-threatening obstruction.

Male dogs are more prone to developing cystine stones. This crystal type is often found in Labrador Retrievers and Newfoundlands.

How are urine crystals diagnosed?

Urine crystals are diagnosed by examining a sample of the dog’s urine under a microscope. If your dog is having urine accidents, your veterinarian will ask you to bring in a urine sample. The best time to collect this urine sample is first thing in the morning. The first voided urine will be the most concentrated sample, since your dog has held her bladder all night while asleep. This sample gives your veterinarian the most accurate information about the urine, before it is diluted by drinking or eating.

To collect your dog’s urine, use a shallow plastic container or soup ladle and slip it under the urine steam while the dog is urinating. A fresh sample is best, so ideally, bring a sample collected the same day. Store the urine sample in the refrigerator until you can bring it in. Your veterinarian will run a complete urinalysis on the sample or send it to a laboratory for evaluation.

What is the treatment for crystalluria?

The treatment for crystalluria depends largely on the type of crystal. Most crystals develop as a result of the diet your dog is eating. Your veterinarian may recommend making changes in your dog’s diet to change the pH of the urine and the mineral composition in order to prevent the formation of urinary crystals.

In some cases, struvite crystals and stones are able to be dissolved by feeding prescription diets. In other cases, diet therapy is not possible, so oral medications may be prescribed. These include potassium citrate to reduce the formation of oxalate stones by binding calcium. Hydrochlorothiazide works to minimize calcium oxalate stone formation by decreasing the amount of calcium excreted in the urine.

DL-methionine acidifies, or lowers, the pH of the urine, which helps to dissolve struvites and prevent their formation. Tiopronin works to bind extra cysteine in the urine and allow it to be eliminated safely. Allopurinol decreases the production of uric acid to decrease the formation of ammonium urate crystals.

If a urinary tract infection is present, your veterinarian will prescribe antibiotics. A culture of the urine is performed to determine the type of bacteria and which antibiotic can best clear the infection.

Recovery from urine crystals depends on the type of crystal and the individual dog’s response to treatment. Urinary tract infections usually resolve quickly with one to two weeks of antibiotics. It is not uncommon for some dogs to need to be fed prescription diets for the rest of their lives.