How common are urate uroliths in female Dalmatians?
Recently, I received a letter from an inquisitive Dalmatian owner which stated in part:
"I have a 9-year-old female Dalmatian that has been diagnosed with a urinary tract infection because of red blood cells found in urine aspirated from her urinary bladder during an annual physical exam. She does not have a problem urinating and her urine appears very clear; it is not bloody. My vet has tried two types of antibiotics (cephalexin first and trimethoprim-sulfa three weeks later). Even though her urine is not bloody, red blood cells are still present in the urinalysis. My vet also prescribed a special diet to prevent urate stones from forming even though no crystals were found in her urine. Is there a probability of urinary stones even though there are no crystals in her urine? Is the urinary tract infection persisting because of stones?"
How would you respond to these questions? Is detection of red cells by urinalysis a reliable index of bacterial urinary tract infection? Does the persistent microscopic hematuria indicate the probability of uroliths? Are urate uroliths common in female Dalmatian dogs? Is there evidence to support a feeding protocol designed to prevent urate uroliths in this dog?
What is the significance of the hematuria?
If RBCs identified in urine of this Dalmatian were associated with bacterial infection, one would expect to also find concomitant evidence of inflammation (i.e. pyuria associated with varying degrees of proteinuria). Furthermore, detection of bacteria in association with pyuria, hematuria and proteinuria would indicate that the inflammatory lesion is active and caused or complicated by infection. If the information provided by the owner about urinalysis is correct, was prolonged treatment of this dog with antimicrobics warranted?
If RBCs were detected in urine sediment of this dog in absence of white cells, noninfectious causes of hematuria should be considered before prescribing antimicrobics. Since the dog was asymptomatic, microscopic hematuria associated with collection of urine by cystocentesis should be investigated (See Diagnote in DVM Newsmagazine, July 1997, page 11S). This mechanism of hematuria could be easily evaluated by performing a urinalysis on a voided urine sample. Collection and analysis of the voided sample should be scheduled a few days after cystocentesis to allow any hemorrhage associated with needle-induced trauma to the bladder time to heal.
Are urate uroliths common in female Dalmatian dogs?
It is common knowledge that Dalmatians are predisposed to urate urolithiasis. But, does this generality apply to both males and females? To answer this question, consider the following epidemiologic data generated by the Minnesota Urolith Center.
From 1981 to 2000, we analyzed 7,560 uroliths retrieved from 7,068 male and 282 female Dalmatians (the gender of 240 Dalmatians was not identified). Of these 7,560 uroliths, 95 percent were composed of urate (especially ammonium urate). However, female Dalmatians comprised only 3 percent of all Dalmatians with urate uroliths; 97 percent occurred in males. The explanation of this marked disparity between the frequency of detection of urate uroliths in male and female Dalmatians requires additional study.
Returning to the question posed at the beginning of this discussion, is there evidence to warrant feeding a diet to prevent urate uroliths in this female Dalmatian? In light of our observations that diagnosis of urate uroliths in female Dalmatians is approximately 30 times less likely compared to male Dalmatians, and in absence of clinical data indicating that this female Dalmatian has urolithiasis, what is your conclusion? Isn't it apparent that the benefit of management protocols designed to minimize urate uroliths in female Dalmatians should be determined after proper evaluation of each individual patient?
Have other types of uroliths been observed in Dalmatians?
The answer is...yes! Not all uroliths formed by Dalmatians are composed of urates. Of the 282 uroliths formed by female Dalmatians and submitted to our Center for analysis, 194 (69 percent) were urate, 6 (2 percent) were struvite, 2 (<1 percent) were xanthine, 32 (11 percent) were compound, and 50 (18 percent) were of mixed composition. Of the 7,068 uroliths formed by male Dalmatians, 6,828 (97 percent) were urate, 30 (0.4 percent) were struvite, 50 (0.7 percent) were xanthine, 19 (0.3 percent) were calcium oxalate, 78 (1.1 percent) were compound, and 96 (1.4 percent) were of mixed composition.
This data underscores the importance of quantitative analysis of uroliths retrieved from all Dalmatians. To emphasize the importance of this recommendation, consider it in the following perspective. If a Dalmatian forms a struvite urolith, the rate of occurrence of struvite is 100 percent for this Dalmatian. This patient is unlikely to benefit from medical protocols designed specifically for management of urate uroliths.
The mission of the Minnesota Urolith Center is to assist in sustaining high-quality veterinary medical care by providing quantitative analysis of uroliths.
This diagnostic service is available without charge, provided uroliths are submitted with relevant data about the patient. To obtain a proper urolith analysis submission from, FAX a request to (612) 624-0751.