Urolith analysis
Uroliths for analysis may be collected with a tropical fish net during the voiding phase of micturition, by aspiration through
a urinary catheter, by voiding urohydropropulsion or by surgery. Uroliths may be submitted to the Minnesota Urolith Center
for quantitative analysis. Additional information may be obtained at our Web site: www.cvm.umn.edu. Click the link to department
and centers to find Minnesota Urolith Center. Alternatively, FAX your request to (612) 624-0751.
Xanthine cannot be distinguished from ammonium urate and other purine metabolites by polarizing light microscopy. Thus, xanthine
may be misidentified if improper methods of analysis are used.
Infrared spectroscopy permits separation of xanthine uroliths from uroliths composed of ammonium urate, sodium urate and uric
acid. Caution must be used to avoid use of allopurinol in patients with xanthine uroliths misidentified as ammonium urate
uroliths.
Treatment and prevention
Medical protocols that consistently promote dissolution of xanthine uroliths in cats have not yet been developed. At this
time, surgery is the most reliable method to remove large active uroliths from the lower urinary tract. However, if urocystoliths
are detected while they are still small enough to pass through the urethra, they may be removed by voiding urohydropropulsion.
In our series, uroliths often recurred within three to 12 months following removal from young and middle-age cats. This is
not surprising since we are currently unable to correct the underlying metabolic defect. Current recommendations for prevention
of recurrence of feline xanthine uroliths encompass reduction in the urine concentration of xanthine and increasing the solubility
of xanthine in urine.
This may be accomplished by combinations of dietary modification, diuresis and alkalinization of urine.
Diets that promote excretion of purines in acidic concentrated urine are likely to increase the risk for xanthine urolithiasis
in susceptible cats. Pending further studies, we recommend moist renal failure diets (such as canned Prescription Diet Feline
k/d, Hill's Pet Nutrition) with the goal of increasing urine volume, minimizing ingestion of purine precursors and minimizing
formation of acid urine. If dry diets are fed, add liberal quantities of water to them. Strive to achieve a urine specific
gravity value less than 1.025.
Perineal urethrostomies may be considered to minimize recurrent urethral obstruction with uroliths in male cats.
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