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Urolithiasis in cats: Evaluation of trends in urolith composition and risk factors (2005-2018)

Kopecny, L., Palm, C. A., Segev, G., Larsen, J. A., & Westropp, J. L. (2021). Urolithiasis in cats: Evaluation of trends in urolith composition and risk factors (2005‐2018). Journal of Veterinary Internal Medicine, jvim.16121.

Uroliths, or bladder stones, occur commonly in domestic cats and may be associated with significant medical and behavioral concerns. Cats with uroliths may experience pain and discomfort, lower urinary disease, and are at risk of lower urinary obstruction. They may also urinate around the hour or outside the litter box. The most common uroliths in veterinary medicine are struvite (magnesium ammonium phosphate) and calcium oxalate. The differentiation of these stones is important, as struvite stones may be dissolved with dietary therapy whereas oxalate stones require mechanical removal.
The purpose of this study was to describe the relative prevalence of feline uroliths submitted to a veterinary urolith laboratory from 2005 to 2018. A secondary objective was to evaluate risk factors for urolithiasis in cats, including age, breed, sex, urolith location, and culture results. It was designed as a retrospective observational study. All urolith submissions from cats between January 1, 2005, and December 31, 2018, were included in the analysis.

Each urolith underwent mineral analysis of each layer using a combination of optical crystallography, polarized light microscopy, and infrared spectroscopy; with X-ray crystallography and liquid chromatography used as needed. If stones consisted of multiple minerals, they were counted multiple times for the purposes of this study. All types of calcium oxalate were included together, as were uric acid and its urate salts.

3940 uroliths were included for analysis. 3187 (80.9%) uroliths were composed of a single mineral type. 105 uroliths had information missing.

Of all stones submitted, 1820 (46.2%) were CaOx‐containing and 1856 (47.1%) were struvite‐containing. Of 1820 CaOx uroliths, 56.6% were composed of CaOx monohydrate only, 0.9% of CaOx dihydrate only, and 42.6% contained both. Over the course of the study, there was a significant decrease in the proportion of CaOx containing uroliths and an increase in struvite containing uroliths. 9.2% of uroliths were urate-containing, of which 49.3% were solely urate. The proportion of urate containing uroliths was stable over time. 7.4% contained apatite, 1.8% dried solidified blood, and 0.5% silica. Assorted other stone types were very uncommon.

Male cats were significantly more likely to have CaOx containing uroliths than female cats, while female cats were more likely to have struvites than males. CaOx stones were more likely to occur in cats >7 years of age, while struvites were more likely in younger cats. No age or sex predisposition was noted for urates.

CaOx stones were more likely to occur in the upper urinary tract than other stone types. 8.8% of stones submitted for culture had positive bacterial growth, of which the most common bacteria were Staphylococcus spp, Enterococcus spp, and E. coli.

The authors concluded that, over time, the proportion of CaOx stones decreased and struvite increased. Other demographic trends were similar to previous reports.

This study had several limitations. The inclusion of a single reference lab recruiting from a single geographic area may have limited the generalizability of this data. Some degree of bias will be present due to the use of lab-submitted samples, as not all stones will have been submitted for analysis. Furthermore, the retrospective nature may also have introduced bias. Recurrent uroliths were not specifically accounted for.

Continued analysis of this large dataset could be beneficial to better understand uroliths trends in cats. This data may also be used to identify areas for further research.

See Also
Cannon AB, Westropp JL, Ruby AL, Kass PH. Evaluation of trends in urolith composition in cats: 5,230 cases (1985‐2004). J Am Vet Med Assoc. 2007; 231: 570‐ 576.

Houston DM, Vanstone NP, Moore AEP, Weese HE, Weese JS. Evaluation of 21,426 feline bladder urolith submissions to the Canadian Veterinary Urolith Centre (1998‐2014). Can Vet J. 2016; 57: 196‐ 201.

Osborne CA, Lulich JP, Kruger JM, Ulrich LK, Koehler LA. Analysis of 451,891 canine uroliths, feline uroliths, and feline urethral plugs from 1981 to 2007: perspectives from the Minnesota Urolith Center. Vet Clin North Am Small Anim Pract. 2009; 39: 183‐ 197.

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Related Terms
Bladder stone