Stalking stones: An overview of canine and feline urolithiasis - Veterinary Medicine
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Stalking stones: An overview of canine and feline urolithiasis
Did you know that a new type of urolith has been found in cats? Should you institute preventive therapy if you identify only crystalluria? Is antibiotic therapy automatically warranted in animals with indwelling urinary catheters? This internist revamps your knowledge on diagnosing, treating, and preventing urolithiasis.


Submitting or saving a recovered urolith, including the nidus, for bacterial culture is recommended in cases in which results of a urine culture are negative or pending, especially in dogs suspected of having struvite uroliths. Submit an entire urolith for bacterial culture in a dry, clean container. Refrigeration is not required for storage or shipping, but, as with all cultures, the specimen should be cultured as soon as possible for optimal results. Antibiotic treatment initiated before urolith recovery may infrequently cause the shell surface and the patient's urine to be sterile; however, viable bacteria may still be present in the urolith's center.10 Although bacteria do not always play a primary role in urolith formation, bacterial infection often accompanies uroliths and represents a complicating factor in treatment.

Often a urolith is not readily available for direct analysis. In those cases, using the patient's signalment to establish any potential breed, age, or sex predisposition together with radiographic examination findings, bacterial culture, and urinalysis results from a fresh, nonrefrigerated sample can provide valuable information regarding potential urolith composition. For example, isolating urease-producing bacteria from the urine is a strong indication of struvite composition, particularly in dogs.

Although identifying specific urine crystals may help determine the urolith composition, several factors must be kept in mind when evaluating the importance of crystals. Many of the commonly recognized crystals can be considered normal findings in urine samples. Their presence does not necessarily indicate that urolith formation will follow or that the composition of any given urolith will match the crystal type identified. In addition, uroliths can be found in some patients that have no identifiable urine crystals. Treatment and prevention plans should always be in response to actual urolith or plug formation and not in response to the presence of crystals alone.


Table 1. Selected Canine and Feline Diets That May Be Used in Urolith and Crystal Dissolution and Prevention Protocols
The following discussion focuses on the characteristics of specific therapeutic and prevention options. Table 1 lists many of the diet options for the dissolution and prevention of canine and feline uroliths. The entries are based primarily on the manufacturer's diet formulation descriptions for nutritionally managing animals with particular crystal and urolith compositions. Few studies are published in peer-reviewed journals that evaluate the efficacy of specific diet formulations in dogs or cats with naturally occurring uroliths.19,20 Table 2 is a quick reference for urolith diagnosis, treatment, and prevention recommendations.


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