ISSN 2398-2950      

Dietetic diet: decreasing risk of urate stones (uroliths)

ffelis
Contributor(s):

Marge Chandler


Pathophysiology

  • Urate calculi form because of increased excretion of urates or uric acid in the urine.
  • Detection of urate crystals or stones strongly suggests the presence of defective metabolism of uric acid due to liver disease, eg with portosystemic shunts   Congenital portosystemic shunt (CPSS)  . 
  • Risk factors for the development of urate stones include increased renal excretion and urine concentration of uric acid. In normal animals, purines are converted to hypoxanthine, which is converted to xanthine and then uric acid. Uric acid is converted to allantoin which is a soluble end product excreted in urine.
  • Increased renal excretion of ammonium may also predispose to urate calculi production. Urinary tract infections with urease producing bacteria ( StaphylococcusProteusE. coliand other enterics bacteria, Mycoplasma) may increase ammonium ions which predisposes to urate calculi formation.
  • Low urine pH is a risk factor since urates tend to form in acidic urine   Urinalysis: pH  . 
  • Idiopathic urate stones also form in 1-4 year old cats but the metabolic defect is unknown.
  • Dietary components may promote stone formation in predisposed patients because dietary purines may be digested, absorbed, and incorporated into the body's purine pool to be eventually excreted in the urine. Extremely low protein diets may encourage urate stone formation by causing hepatic dysfunction and increased uric acid excretion.
  • Hepatic disease (eg portocaval shunts, cirrhosis   Liver: cirrhosis  ) results in reduced conversion of uric acid to allantoin which increases urate and ammonium excretion in the urine.
  • Medical management (dissolution and prevention) of urate uroliths consists of feeding a diet which has reduced levels of animal-source proteins (particularly purine, a nucleotide that is metabolised into uric acid), oral urinary alkalinisers, and allopurinol   Allopurinol   (a xanthine oxidase inhibitor that reduces urinary uric acid levels).
  • For animals with portosystemic shunts, diets for liver disease should be fed and treatment addressed as appropriate for the patient.

Dietary requirements for patients without liver disease

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Special considerations

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Recipes (for pets without liver disease)

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Labato M A (2001) Managing urolithiasis in cats. Vet Med 96 (9), 708-718 VetMedResource.
  • Osborne C A, Lulich J P, Thumchai R et al (1996) Feline urolithiasis. Etiology and pathophysiology. Vet Clin North Am Small Anim Pract 26 (2), 217-232 PubMed.

 

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