Risk and protective factors
What is the underlying reason for the gradual but dramatic change in the mineral composition of canine uroliths? Although
several hypotheses have been proposed to explain this phenomenon, to date none have been proved. Available evidence suggests
an interaction between 1) demographic risk factors such as breed, age, gender, anatomy and genetic predisposition and 2) environmental
risk factors such as sources of food, water, exposure to certain drugs and living conditions. Some factors may increase the
risk for urolith formation, and some factors may be protective.
Figure 1: MAP = Magnesium ammonium phosphate, or struvite; CaOx = calcium oxalate; Capoh = calcium phosphate.
Please note that not all risk and protective factors are of equal importance. It is apparent that each contributing risk or
protective factor may play a limited or a significant role in the pathogenesis of urolithiasis. The chance of developing a
specific type of urolith when exposed to one or more risk or protective factors is often expressed in terms of numerical probabilities
(so-called odds or odds ratios).
Figure 2: MAP = Magenesium ammonium phosphate, or struvite; CaOx = calcium oxalate; CaPO4 = calcium phosphate; Cmpd = compound.
When used in a qualitative rather than quantitative way, the significance of risk or protective factors should not be assigned
an "all or none" or "always or never" interpretation. In many situations, each risk factor contributes a limited role to the
development of urolithiasis. In fact, in some situations, they may not be a factor in every exposed patient. Furthermore,
identifying one event in a chain of etiologic events is not the same as identifying the entire etiologic chain.
Figure 3: MAP = Magenesium ammonium phosphate, or struvite; CaOx = calcium oxalate; CaPO4 = calcium phosphate; Cmpd = compound.
Why identify risk and protective factors?
Our interest in recognizing the association of specific risk and protective factors with urolithiasis is related to 1) identifying
healthy but susceptible populations of animals and trying to minimize their exposure to these risk factors, 2) identifying
healthy but susceptible populations and trying to enhance their exposure to protective factors and 3) facilitating detection
and treatment of subclinical urolithiasis that has already developed in susceptible patients.
With support of an educational gift from Hill's Pet Nutrition, studies are in progress at the Minnesota Urolith Center to
identify risk and protective factors associated with calcium oxalate, struvite, urate, cystine, calcium phosphate and silica
uroliths in dogs and cats. To learn more about our studies and how you can participate in them, visit our Web site at
http://www.cvm.umn.edu/. Click the Directory link to find the Minnesota Urolith Center. We are providing online submission, e-mail notification and
electronic retrieval of results. With a database of more than 600,000 samples, we are able to provide the veterinary community
with the latest information on urolith trends, treatment and prevention suggestions.
Dr. Osborne, a diplomate of the American College of Veterinary Internal Medicine, is professor of medicine in the Department of Small
Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota.