How common are feline kidney stones?

From 2022 through 2023, the Minnesota Urolith Center analyzed stones from over 45,000 cats.  1.7% of urolith submissions were stones from the kidney or ureter. Of these, 76% were calcium oxalate, 12% were struvite, 3% were urate, 3% were solidified blood, 2% were mixed, and 4% were uncommon stones.   The average age of cats was 7.2 ± 3.7 years (min to max = 0.3 to 20 years).

 

Does this mean that kidney stones are uncommon?  In a recent retrospective study, the radiographic prevalence of upper urinary tracts stones in cats residing in the United States was 2.7 percent in cats less than 6 years old (5/183) and 10.2% in cats ≥ 6 years old (52/510).1   Estimating stone prevalence from medical imaging has limitations. The decision to acquire imaging depends on the likelihood that the attending clinician will find them useful, that the owners are willing to pay for them, and that radiographic procurement is safe for the cat.  In addition, not all stones are radiopaque.  

 

Why are so few kidney stones submitted for analysis?  The majority of kidney stones do not appear to cause clinically significant disease requiring their removal and subsequent analysis.  The ACVIM urolith consensus advises that “only those nephroliths contributing to outflow obstruction, recurrent infection, pain, and those enlarging to the point of causing renal parenchymal compression, should be considered for removal; uroliths amenable to medical dissolution (e.g. struvite) should be dissolved.2 (Feline Struvite Dissolution )

 

Our clinical advice: An adverse consequence of some kidney stones is ureteral obstruction and acute kidney injury.  When nephroliths are detected, develop a monitoring plan to assess active disease (e.g. infection, obstruction, hematuria, pain) and progression (e.g. rising azotemia, urolith movement).  When ureteroliths are detected, develop a plan to assess active disease (e.g. infection, obstruction, pain) and urolith movement down the ureter.  Include medical imaging and owner assessment of pain, appetite and hematuria.  When calcium oxalate is the predicted stone composition (i.e. stones of similar radiopacity to bone), follow our calcium oxalate prevention guidelines to minimize stone growth.  (Feline Calcium Oxalate Uroliths )

In cats with chronic kidney disease, prioritize nutrition and therapy guidelines to minimize progression of kidney disease over stone prevention recommendations.

 

1. Wightman et. al. Vet Med Sci 2016;2:255

2. Lulich et. al. J Vet Intern Med 2016;30:1564