Lower urinary tract disease is a common ailment in domestic cats. Though many causes of lower urinary disease exist (stones, FIC, infection, etc), crystalluria is among the most common. Struvite (magnesium ammonium phosphate) crystals are potentially the most common variant in domestic cats. These crystals may be associated with minor irritation or can contribute to full lower urinary tract obstruction. They are also a predictor of the formation of lower urinary stones. While diet is known to be a contributor to crystal formation, other effects (such as sex, season, breed, and geographic location) may also lead to their formation. Hematuria (the presence of blood in the urine) is a marker of inflammation or irritation associated with the presence of crystals.
This study was designed as a retrospective, case-control study investigating correlations between diet, signalment, geographic and clinical factors and the development of struvite crystalluria. Data was collected from electronic health records of cats presenting to primary care veterinary hospitals across the USA from 2007 to 2011.
Cats with a medical record diagnosis of crystalluria were included. Only the first visit for which crystalluria was noted was included. Cats were excluded if this was their first veterinary exam, if they had a previous diagnosis of hematuria or CKD, or if they were fed a “urinary” diet. Control cats were randomly selected using a rate matching system from cats with a urinalysis unrelated to urolithiasis/crystalluria at a rate of 2 controls per case.
Thirteen thousand two hundred thirty-seven cats were identified with crystalluria, of which 7621 (57%) had struvite crystals. 4032 of these had concurrent hematuria. Cases originated from 717 hospitals in 43 states. Both univariate and multivariate statistical models were used to investigate correlations between hematuric struvite crystalluria (HSC) and a multitude of clinical and demographic variables.
In univariate models, several factors were associated with an increased risk of crystalluria. These included increasing age, male sex, obesity, number of dogs/cats in the household, a history of cystitis, and being fed a dry diet. Diabetes mellitus decreased the risk of HSC.
On multivariate analysis, age, diet, neuter status, body condition, urine protein concentration, urine pH, presence of pyuria or bacteriuria, or a previous diagnosis of cystitis remained predictive of HSC. Interestingly, young cats fed a dry diet were at increased risk, while in older animals this risk decreased.
It is important to note that these findings are correlational and not causational. For example, the presence of increased protein in the urine may be a result of crystalluria, and not a cause. Hematuria in many of these samples may also have been a result of collection (ie cystocentesis) and not necessarily related to the disease process.
The authors suggest that several of the factors in this study may be helpful to predict the cats most at risk for lower urinary disease caused by HSC. Further work is needed to investigate several of the findings, including the relationship between age, dietary moisture, and the risk of HSC. MRK)
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