Calcium Oxalate Crystals in Dog Urine

By Tess Thompson

Bladder stones are mineral deposits that form in the urinary bladder of the animal. Some of these stones initially look like crystals, but over time turn into stone-like substances that can potentially block the urinary passage, causing canine or feline urinary incontinence or cessation of urine. Instances where there is a disturbance in pH balance by increased absorption of calcium, or intake of an improper type of calcium, results in minerals forming crystals in the urine. Stones then start to form around a central point or locus of an infection-- in this case, the urinary tract infection. Urinary tract infection In dogs calcium oxalate stones are the most common.

Calcium oxalate stones and struvite are the two most common types of bladder stones found in the urinary tract. The other types, urate, silicate, cystine, and calcium phosphate stones, are relatively rare. Urinalysis can indicate the prevalence of stones, and the pH balance gives a hint of the type of stone that can be expected. However, unless the stone is extricated by surgery or forceful expression and examined, there is no surety of the type of stone.

Calcium oxalate stones form in acidic to neutral urine. Calcium oxalate stones are further divided into two types that occur naturally in dogs- calcium oxalate monohydrate and calcium oxalate dehydrate. Dogs with a condition called hypercalcemia-- the presence of abnormally high levels of calcium in the blood-- are more likely to develop these types of stones. Hypercalcemia is usually the result of excessive bone re-absorption in hyperparathyroidism or excessive bone destruction in older dogs.

Certain dog breeds are genetically predisposed to calcium oxalate stones. These include Miniature Schnauzers, Lhasa Apsos, Yorkshire Terriers, Miniature Poodles, Shih Tzus, and Bichon Frises. The condition is more prevalent in male dogs rather than female dogs.

Prevention of calcium oxalate stones is difficult through dietary modifications alone. A diet that is low in proteins and oxalates and high in magnesium, phosphorous, and calcium is recommended. This works in two ways:

  • Increased magnesium and phosphorous reduces the amount of calcium in the urine.
  • Increased calcium in the diet limits the absorption of oxalates from the intestines.

Ingesting potassium citrate helps in preventing calcium oxalate stones, since calcium bonds to citrate creating calcium citrate, a compound that is soluble. This prevents calcium from binding with oxalate to create calcium oxalate, a compound that forms deposits in urine and ultimately results in bladder stones. Potassium citrate also forms a soluble compound with oxalates, reducing acidity in the urine, and is recommended as a preventive measure and treatment.

Diuretics, especially of the thiazide class, can help in two ways by increasing the amount of urine and reducing the calcium content.

No matter what you do, preventing the recurrence of bladder stones is difficult. The best you can do to try and reduce canine and feline urinary infections in your pet is to ensure good bladder health. Monitor their recurrence through radiography and try and flush out calcium oxalate crystals before they become large.


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