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Calcium Oxalate Crystals in Dog Urine

Calcium Oxalate Crystals in Dog Urine

Calcium oxalate crystals in dog urine may cause concern in dog owners when lab results reveal such finding. However, calcium oxalate dihydrate crystals may be seen in healthy dogs in small amounts and their presence are not always necessarily an indication of problems unless the affected dog shows signs of possibly having stones. Because dogs are sometimes stoic and not always show signs indicative of disease processes, further investigation by the vet may be helpful to rule out stones and kidney issues.

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Crystals in Dog Urine

Crystals in dog urine (crystalluria) are detected through a urine test by looking at the urine sample under a microscope. Crystals are simply mineral sediments, that can potentially develop into mineral stones which are medically known as uroliths.

Depending on the type of crystals found, their composition varies. Crystals can develop due to different and specific reasons and each type requires a different treatment approach.

Types of crystals in a dog's urine include: struvite crystals, magnesium ammonium phosphate crystals, calcium oxalate crystals, cystine, urate and silica crystals.

While some dogs with bladder crystals or stones may show no particular signs, others can develop lower urinary tract pain, difficulties urinating or frequent urination in small amounts. Blood in the urine (hematuria) is also another common sign considering that when stones rub against the bladder wall, they may cause erosion to the tissue causing bleeding.

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Left untreated, crystals in a dog's urine may cause annoying urinary tract infections, stone formation and expensive surgeries (even in the range of $1200 to $2000). However, this is not a rule: crystalluria is not necessarily synonymous with the presence of stones.

Calcium Oxalate Crystals in Dog Urine 

Calcium oxalate in a dog's urine

Calcium oxalate crystals in dog urine

Calcium oxalate crystals are one of the most common type of crystals found in a dog's urine. They are frequently found in male dogs over the age of five with miniature schnauzers, Lhasa Apso, Maltese, Yorkshire terriers, miniature poodles, dachshunds, Chihuahuas, bichon frise' and shih-tzu commonly predisposed.

Calcium oxalate crystals are found in acid urine of dogs (pH lower than 6.5) with high levels of calcium in the blood. They are most commonly found in the bladder and less often in the dog's upper urinary tract.

Calcium oxalate crystals in dog urine can be the result of the dog's diet and/or they may be manufactured by the body. Dogs with a history of being on some type of steroids (ex. prednisone, dexamethasone, methylprednisone) or diuretics (ex. Lasix, hydrochlorothiazide) are predisposed.

Now, when crystals are detected, it's important to point out the quality of the urine sample obtained. Old, non refrigerated and improperly stored samples by dog owners may yield false positives. It may help to evaluate presence of crystalluria on a fresh urine sample collected on the spot. The persistent presence of crystals usually represents a greater risk for stone formation compared to the occasional presence of crystals.

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Did you know? Although struvite stones were the prevalent types of stones found in the 1980s, there has been a significant increase in the number of calcium oxalate stones (CaOx) in dogs and cats in North America. Just to get a feel of statistics, in the USA, calcium oxalate stones in dogs increased dramatically from 5 percent in 1981 to an astounding 42 percent in 2005.


"Calcium oxalate crystalluria is also a common finding in healthy dogs and cats; as with struvite crystalluria, in the vast majority of patients calcium oxalate crystals do not merit intervention."~ Dr. Barrak Pressler

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At the Vet's Office 

After a urine test reveals presence of calcium oxalate crystals in a dog's urine, the vet may wish to perform more detailed veterinary exams especially in dogs exhibiting symptoms suggestive of presence of bladder stones. Upon palpation, experienced vets may detect presence of large stones in a dog's bladder.

Next, the vet may request x-rays which can pick up the presence of any stones. On xray, stones are easy to detect because they are dense and therefore easy to detect. However, on ultrasound it may be possible to see stones that may be difficult to identify on x-rays.

Dogs may also be screened for diseases known to cause excess calcium in the blood or urine (e.g. hyperparathyroidism, chronic renal failure, exposure to antifreeze, Cushing's disease, paraneoplastic hypercalcemia, that is, cancer that causes increased calcium levels such as lymphoma and various types of carcinoma). Blood tests to run for a more in-depth insight may include serum calcium, BUN, and creatinine.

Since calcium oxalate crystals are seen in dogs whose urine is too acid, the use of products meant to raise the pH of the urine, so that it's above the neutral level of 7, may be suggested. Potassium citrate may be prescribed by the vet. Dog owners can use pH paper to regularly test the dog's urine. It's important to avoid producing too high a pH as a too high pH can produce different types of crystals and stones.

Encouraging drinking is also important. Diet-wise, vets may prescribe urinary diets such as that are low in protein and oxalate content, such as Hill's Prescription Diet u/d. Calcium oxalate stones in dogs can take some time to go away.

Prevention of calcium oxalate crystals in dogs is difficult because at this time the exact factors responsible for their
formation are not yet completely understood. It helps to check the urine on a routine basis after starting a new diet to monitor the situation before new stones form. Should stones ever form, surgery may be needed.

Did you know? Oxalobacter formigenes is a type of intestinal bacteria that ingests oxalate. By consuming oxalate in the dog's intestine, less oxalic acid is excreted in urine. To preserve healthy populations of this bacteria, avoid excessive use of use of antibiotics.


" Typically if I have a dog that is getting Calcium oxalate crystals I look at the PH of the urine. If the PH is low then that tells me that the urine is becoming to acidic. If that is the case then I try to make the urine more basic. Typically to do this I would prescribe a supplement called Potassium Citrate to attempt to do this. "~Dr. Alleyne, veterinarian

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  • Canine and feline urolithiasis: Examination of over 50 000 urolith submissions to the Canadian Veterinary Urolith Centre from 1998 to 2008 Doreen M. Houston, Andrew E.P. Moore, CVJ / VOL 50 / DECEMBER 2009
  • Minnesota Urolith Center, University of Minnesota, Calcium oxalate Urolithes

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