Urolith Advice and Facts

The 2 Millionth Urolith: How to Pick the Best Diagnostic Test for Urate
2 millionth urolith from a dog composed of 100% ammonium urate

In the summer of 2026, the Minnesota Urolith Center received its 2 millionth stone. The composition was 100% ammonium urate, and the stone came from a 4-year-old male neutered Shih Tzu. Urate comprises 5% of uroliths from dogs and 7% from cats. The most common causes of urate stones are portosystemic shunting and hereditary hyperuricosuria (HUU). 

How do you pick the best diagnostic test for a pet with urate uroliths?

In order to decide whether to start with bile acids testing to screen for portosystemic shunting versus genetic testing to screen for HUU, consider the following factors:

  1. Other clinical signs or abnormalities - Bile acids testing should be performed in dogs and cats with urate stones and other clinical evidence for shunting, such as those with gastrointestinal or neurological signs (present in ~50%), elevated liver enzymes (~50% have increased ALT), or abnormal liver function values (~30-40% have low BUN or cholesterol; ~10-15% have low albumin). 
    • The absence of clinical signs and biochemical abnormalities does not rule out shunting. However, if bile acids are within the reference intervals for both the pre- and post-prandial values, HUU is the most likely cause of the urate stones.
  2. Age - For cats, a young age is a reason to consider bile acids testing. The median age of cats with urate from portosystemic shunting is 2-3 years, which is younger than those without shunting. Age is less helpful in dogs with urate because the median age for those with shunting versus HUU overlaps (3-4 and 4-5 years, respectively). 
  3. Breed - Breed is an important consideration in dogs, as the breeds at highest risk for congenital portal vascular anomalies largely differ from those at highest risk for HUU. The table below shows the top 30 dog breeds for urate urolith submissions, separated by reported breed predispositions for portal vascular anomalies versus HUU. 
top 30 dogs breeds for urate uroliths separated by most likely risk factors

For cats, the Egyptian Mau and European Shorthair are particularly high risk. While HUU is suspected in these breeds, genetic testing is not currently available for cats.

What does this mean for the 2 millionth urolith dog?

Given his breed (Shih Tzu), portosystemic shunting is the most likely cause of the urate uroliths, and bile acids testing is recommended.

Resources

  1. Albasan H, et al. Risk factors for urate uroliths in cats. J Am Vet Med Assoc 2012;240:842.
  2. Dear JD, et al. Feline urate urolithiasis: a retrospective study of 159 cases. J Feline Med Surg 2011;13:725.
  3. Donner J, et al. Genetic prevalence and clinical relevance of canine Mendelian disease variants in over one million dogs. PLoS Genet. 2023;19:e1010651.
  4. Tobias KM, Rohrbach BW. Association of breed with the diagnosis of congenital portosystemic shunts in dogs: 2,400 cases (1980-2002). J Am Vet Med Assoc. 2003;223:1636-9. 
  5. Walton-Clark M, et al. Retrospective analysis of the incidence and clinicopathological findings associated with ammonium urate urolithiasis in dogs with congenital portosystemic shunts: 363 cases (2010-2023). J Small Anim Pract. 2025;66:248-257. 

See also our detailed Canine Urate Uroliths  and Feline Urate Uroliths recommendations

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