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Crystals in the Urine in Cats

Crystalluria in Cats

Crystalluria is a medical condition where crystals are expelled into the urine. The detection of urinary crystals is not synonymous with kidney stones or the clinical signs associated with them, nor is detection of urine crystals irrefutable evidence of a stone-forming tendency, but there is some association with an increased risk for kidney stones in animals that are afflicted with crystalluria, and crystals in the urine can be an indication of kidney stones (also referred to as renal stones). Crystals form only in urine that is, or recently has been, supersaturated with crystallogenic substances.

Proper identification and interpretation of urine crystals is important for determining a medical strategy for treating the condition, since certain crystal types may indicate an underlying disease. Evaluation of urine crystals may aid in (1) detection of the disorders that predispose the animal to stone formation, (2) estimation of the mineral composition of the stones, and (3) evaluation of the effectiveness of the medical procedures initiated to dissolve or prevent the stones.

Crystalluria in animals with anatomically and functionally normal urinary tracts is usually harmless because the crystals are eliminated before they grow large enough to interfere with normal urinary function. Even so, they represent a risk factor for kidney stones.

Crystals that form in the urine following elimination or removal of urine from the patient often are of little clinical importance (i.e., crystals formed in the urine after leaving the body). Identification of crystals that have formed in vitro (in a lab environment) will not justify therapy. Situations that will require further follow-up are instances where some types of crystals are detected in patients without symptoms (asymptomatic); when large aggregates of crystals (e.g., calcium oxalate or magnesium ammonium phosphate) in apparently normal individuals are detected; or, when detection of any form of crystals in fresh urine collected from patients with confirmed kidney stones may have diagnostic, prognostic, or therapeutic importance.

Breeds that are prone to calcium oxalate crystals in the urine are Burmese, Himalayan, and Persian cats.

Symptoms and Types

The sole symptom of crystalluria is the presence of detectable crystals in freshly expelled urine. Other related symptoms are those caused by concomitant kidney stones.

Causes

  • Concentration of crystallogenic substances in urine (which in turn is influenced by their rate of excretion and urine concentration of water)
  • Urine pH is off balance – acidic or alkaline levels need to be balanced
  • Lack of solubility of crystallogenic substances in urine
  • Excretion of diagnostic agents (e.g., radiopaque contrast agents) and medications (e.g., sulfonamides)
  • Dietary influence - hospital diet may differ from home diet; timing of the sample collection (fasting versus postprandial) may influence evidence of crystalluria

Diagnosis

X-ray or ultrasound may be able to detect some stones, but urinalysis will be the major tool for analysis of crystalluria.

 
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