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.


Increase water intake

Increasing the water intake in dogs and cats is an important part of treating and preventing uroliths. Feeding a patient a canned diet or adding water to dry food increases urine volume, decreases the concentration of urine minerals potentially involved in urolith formation, and helps eliminate these minerals through more frequent urination.11,12 Successful dilution can be evaluated by periodically checking a patient's urine specific gravity to see if it remains < 1.020.13-15

Consider new minimally invasive methods

New techniques combining interventional radiographic and endoscopic procedures have enhanced the diagnosis and removal of uroliths.16,17 Fluoroscopy, ultrasonography, and endoscopy are used to identify and retrieve uroliths located virtually anywhere in the urinary tract. This combination of methods can be used to place stents to relieve urolith-related obstruction and to facilitate antegrade passage of uroliths. The development of percutaneous approaches has improved accessibility to sites such as the renal pelvis (percutaneous nephrolithotomy), allowing ultrasonic and laser lithotripsy to be performed with less damage to the surrounding tissues. Although most of these techniques have limited availability at veterinary facilities, continued success in treating uroliths with these minimally invasive methods should increase their availability to veterinary patients in the coming years.

Identify urolith composition and bacteria

Catheter-assisted urolith retrieval
Because urolith composition is an important factor in determining the treatment and prevention options, it is important to accurately identify urolith composition whenever possible. The most direct method of determining urolith composition is analyzing the urolith itself. Uroliths can be collected for submission through surgical intervention, routine voiding, voiding urohydropropulsion, or catheter-assisted retrieval. (For more information on this technique, see the boxed text titled "Catheter-assisted urolith retrieval.")

Analysis can be either qualitative or quantitative. Qualitative analysis is performed by several laboratories and can determine the approximate urolith composition. Quantitative analysis uses more sophisticated techniques to determine the exact composition of the urolith's nidus (nucleus), body, and shell, including the exact percentages of mixed components. Quantitative analysis is the preferred method for determining urolith composition because it provides a much more accurate analysis when compared with qualitative methods and greater guidance in developing appropriate therapeutic and preventive plans.18

For best results, submit the entire urolith in a dry, unbreakable container. If the patient has multiple uroliths, submit either all the uroliths recovered or a representative assortment for quantitative analysis. Urolith fragments may be collected for quantitative analysis after lithotripsy by using stone baskets or grasping instruments at the time of the procedure or by collecting voided urine after the procedure and pouring it through a tea strainer.

The Minnesota Urolith Center at the University of Minnesota College of Veterinary Medicine will perform quantitative analysis of uroliths at no charge except for standard shipping fees. Submission forms and information can be obtained at http:// Quantitative analysis can also be performed for a fee at the Urinary Stone Analysis Laboratory at the University of California at Davis School of Veterinary Medicine or at human laboratories such as the Urolithiasis Laboratory at the Baylor College of Medicine in Houston or the Louis C. Herring and Company laboratory in Orlando, Fla.


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