Knowledge of urolith composition is important because contemporary methods of detection, treatment and prevention of the underlying
causes of urolithiasis largely depend on knowledge of urolith composition.
The following discussion is based on quantitative analysis of 36,032 canine uroliths submitted to the Minnesota Urolith Center
In 1981, calcium oxalate was detected in only 5 percent of canine uroliths submitted to the Minnesota Urolith Center, whereas
struvite (magnesium ammonium phosphate) was detected in 78 percent.
However, evaluation of the prevalence of different types of minerals in canine uroliths during successive years reveals a
gradual and consistent increase in calcium oxalate uroliths, and a gradual and consistent decline in struvite uroliths (Figure
In fact, by 2003 the prevalence of calcium oxalate (41 percent) was approximately equal to struvite (40 percent). In 2004,
calcium oxalate (41 percent) surpassed struvite (39 percent). In 2005, calcium oxalate was detected in 41 percent of urolith
submissions while struvite was detected in (38 percent).
In other words, from 1981 to 2006, struvite uroliths declined by approximately 43 percent compared to a 78 percent increase
for calcium oxalate (Figure 1).
Trends in 2006
What would be your estimate of the occurrence of calcium oxalate and struvite urolith submissions to the Minnesota Urolith
Center in 2006? Even though the total submission (36,032) of canine uroliths was 3,147 more than for the year 2005, in 2006
the frequency of occurrence of calcium oxalate (41 percent) and struvite (39 percent) remained approximately the same (Table
1; Figs. 1 and 2).
Recall that the frequency of feline calcium oxalate and struvite occurrence during the same period was similar. (For additional
details related to feline uroliths and feline urethral plugs, refer to the Diagnote titled "Changing trends in composition
of feline uroliths and feline urethral plugs," February 2007 issue of DVM Newsmagazine.)
Table 1 Quantitative mineral composition* of 36,032 canine uroliths — 2006
Risk and protective factors
What is the underlying reason for such a dramatic change in the composition of canine uroliths? Although several hypotheses
have been proposed, none has been proven to date. 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 be protective.
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 of the risk or protective factors often is expressed in terms of numerical probabilities
(so-called "odds" or "odds ratios").
When used in a qualitative (rather than a quantitative) way, the significance of risk or protective factors should not be
assigned an "all or none" or "always or never" interpretation.