Summary

Urine is liquid waste made by the kidneys. Common elements of urine include chemicals toxic to the body (e.g. urea), electrolytes (e.g. potassium), salt and other minerals, and water.

Urine pH can be acidic (low) or alkaline (basic, high) depending on many factors, including diet, filtered waste, and infection. The pH can affect the contents and concentration of urine. Sometimes urine will contain other elements such as crystals, sediment or bladder stones, white blood cells or pus, bacteria, urinary tract cells, or blood.

Urine crystals, also known as crystalluria, are the microscopic formation of certain minerals into solids within the urine. 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 very dilute and clear) or the urine sample itself is not fresh. Temperature, diet, and urine pH also potentially affect crystal formation in the urine.

Crystals in the urine can mean a bladder (or rarely kidney) stone is present or that the urinary environment is perfect for bladder stone formation. The minerals continue to connect and solidify with each other, forming a stone that looks similar to what you might find in nature.

Several types of crystals and stones are associated with the bladder, depending on the urine’s make up and factors outside the urinary tract (e.g. genetics, diet). Examples of crystal types include:

  • Struvite
  • Calcium Oxalate
  • Cystine
  • Urate
  • Xanthine
  • Silica

The two most common types of urine crystals in dogs and cats are struvite (also known as magnesium ammonium phosphate or MAP) and calcium oxalate.

Struvite crystals in dogs most often form because of a urinary tract infection. Common bacteria that invade the urine create an environment with a higher (more alkaline) pH which helps the bacteria thrive. Struvite crystals form easily at higher urine pH, and struvite stones can form quickly if enough crystals develop.

In cats, struvite crystals are more likely to form in sterile, or noninfected urine. Veterinary scientists aren’t sure why this is, but as with dogs, high urine pH is a factor.

Less is known about why calcium oxalate crystals form in dogs and cats. A direct cause isn’t often found. Calcium oxalate crystals are more likely to form in acidic urine and can occur when increased calcium occurs in the body (e.g. through the diet).

Symptoms and Identification

Dogs and cats with crystalluria may not show any sign, but some possible symptoms include:

  • Straining to Urinate
  • Passing Dark, Concentrated &/or Bloody Urine (especially if urinary tract infection and/or bladder stones are also present)
  • Poor Appetite
  • Painful Tummy

Microscopic examination of a fresh urine sample will show the crystals and generally allow your vet to identify the type. It may also show bacteria and red and white blood cells. A urinalysis will be performed to make sure an infection is not present. If an infection is found, sometimes a culture and sensitivity will then be performed on the urine to make sure the right antibiotic is used to kill the bacteria.

X-rays may be needed if bladder stones are suspected – most, but not all types of bladder stones show up on X-ray. Sometimes kidney stones will also be seen. An abdominal ultrasound may be necessary in some cases to see other changes that could be related to crystalluria, or to look for stones that are not visible on X-ray.

Affected Breeds

In dogs, males seem to be affected with calcium oxalate crystals more often and females are more commonly affected by struvite crystals. Urine crystals can form at any age.

The most common dog breeds to develop calcium oxalate crystals include:

The most common breeds to develop struvite crystals include:

In cats, the average age of struvite crystalluria is 7 years. No breeds have been specifically reported to be more likely than others to be affected by struvite crystals. Calcium oxalate crystals are more common in middle-aged to older, neutered males. Persian and Himalayan breeds may be more likely than other breeds to be affected. 

Treatment

Treatment depends on the type of crystals, factors associated with their formation, and if bladder stones are also present. For cats and dogs with crystalluria because of a urinary tract infection, antibiotics may be prescribed (with or without a urine culture).

If stones have developed, surgery to remove the stones may be necessary. In some cases, a prescription diet may be prescribed to help dissolve the stones and crystals.

For calcium oxalate crystals, treatment is less straight forward because the crystals cannot be dissolved with diet. If no stones are present, changing to a prescription diet may help prevent stone development. Significantly increasing water intake regardless of crystal type may help dilute the urine and flush crystals from the body.

Veterinary Cost

  • Exam, Urinalysis, & Microscopic Urine Assessment Ranges from $100-200
  • Urine Culture Ranges from $120-250
  • X-rays Cost $75-300
  • Ultrasound Costs $300-450
  • Average Cost of Antibiotics is $50-75 (this varies quite a bit based on size of the pet & type of infection)
  • Prescription Veterinary Diets are Approximately $25-75/ Month (depending on size of pet & dry or wet food varieties)
  • Surgery to Remove Bladder Stones can Cost Between $750-2,000

Prevention

Struvite crystalluria can be prevented through prescription diets that help maintain a certain urine pH and control urine mineral levels. Feeding high moisture foods and allowing plenty of access to water will help keep the urine dilute which keeps the urinary tract flushed and minimizes the risk of minerals solidifying.

For pets who have struvite crystalluria because of bacteria, once the bacteria are gone, the urine may return to a normal pH and no other preventive measures may be needed.

Calcium oxalate crystalluria is difficult to prevent and pets relapse frequently – one veterinary study showed a 50% relapse rate within 2 years for dogs and a 7% relapse rate for cats. As with other types of crystalluria, keeping your pet well-hydrated is important for prevention.

Some veterinarians recommend medications to prevent acidic urine, but this does not always prevent crystal or stone formation. Further, if the urine pH becomes too high, it puts pets at risk for other types of crystal formation. Some prescription diets are available to help prevent calcium oxalate crystalluria, but they may not be safe for all dogs to eat, so discuss these options with your vet.

References

Graham PA: Urinalysis. Textbook of Veterinary Internal Medicine. 8 ed. Elsevier, St. Louis MO 2017 pp. 283-288.

Lulich JP, Osborne CA: Lower Urinary Tract Urolithiasis in Dogs. Textbook of Veterinary Internal Medicine. 8 ed. Elsevier, St. Louis MO 2017 pp. 1996-2004.

Labato MA: Lower Urinary Tract Urolithiasis - Feline. Textbook of Veterinary Internal Medicine. 8 ed. Elsevier, St. Louis MO 2017 pp. 2005-2010.

Low WW, Uhl JU, Kass PH, et al: Evaluation of trends in urolith composition and characteristics of dogs with urolithiasis: 25,499 cases (1985-2006). J Am Vet Med Assoc 2010 Vol 236 (2) pp. 193-200

Houston DM, Moore A P: Canine and feline urolithiasis: examination of over 50 000 urolith submissions to the Canadian veterinary urolith centre from 1998 to 2008. Can Vet J 2009 Vol 50 (12) pp.1263-1268.

Albasan H, Osborne CA, Lulich JP, et al: Rate and frequency of recurrence of uroliths after an initial ammonium urate, calcium oxalate, or struvite urolith in cats. J Am Vet Med Assoc 2009 Vol 235 (12) pp. 1450-1455.

Lulich JP, Osborne CA: Changing paradigms in the diagnosis of urolithiasis. Vet Clin North Am Small Anim Pract 2009 Vol 39 pp. 79-91.

Langston C, Gisselman K, Palma D, et al: Diagnosis of urolithiasis. Compend Contin Educ Vet 2008 Vol 30 pp. 447-450.

Lulich JP, Osborne CA, Albasan H, et al: Trends in the global proportions of canine uroliths. Vet Rec 2013 Vol 172 pp. 363.

Osborne CA, Lulich JP, Kruger J, et al: Analysis of 451,8891 canine uroliths, feline uroliths and feline urethral plugs from 1981 to 2007: perspectives from the Minnesota Urolith Center. Vet Clin North Am Small Anim Pract 2009 Vol 39 pp.183-197.

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