Pathophysiology

• Urate calculi form because of increased excretion of urates or uric acid in the urine.
• Dalmatian dogs Dalmatian and bulldogs Bulldog have a higher frequency of urate stone formation than other breeds. Genetic factors play a role in Dalmatians and bulldogs.
• Detection of urate crystals or stones in breeds other than the Dalmatian strongly suggests the presence of defective metabolism of uric acid due to liver disease, eg with portosystemic shunts Congenital portosystemic shunt (CPSS). Breeds that are predisposed to portosystemic shunts (eg Yorkshire terriers Yorkshire Terrier ) may also form urate stones.
• 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.
• Dalmatians cannot oxidize uric acid to allantoin completely. They are unable to efficiently transfer uric acid inside the hepatocyte. The proximal renal tubules of Dalmatians also reabsorb less uric acid than normal dogs. All Dalmatian dogs excrete high levels of urate in urine but not all develop associated uroliths.
• Increased renal excretion of ammonium may also predispose to urate calculi production. Urinary tract infections with urease producing bacteria ( Staphylococcus, Proteus, E. 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.
• 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 in Dalmatians or other genetically prone breeds without hepatic disease 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

Special considerations

Recipes (for pets without liver disease)

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.
• Bartges J W, Osborne C A, Lulich J P et al (1999) Canine urate urolithiasis. Etiopathogenesis, diagnosis, and management. Vet Clin North Am Small Anim Pract 29 (1), 161-91 PubMed.
• Sorenson J L, Ling G V (1993) Diagnosis, prevention, and treatment of urateurolithiasis in Dalmatians. JAVMA 203 (6), 863-869 PubMed.