Felis ISSN 2398-2950


Synonym(s): Kidney stone, urolithiasis

Contributor(s): Penney Barber, Samantha Taylor


  • Uncommon; sometimes incidental finding, lodged in renal pelvis.
  • Cause: nephroliths of different composition possible with variable causes.
  • Signs: asymptomatic or can occasionally obstruct urinary flow.
  • Diagnosis: radiography, ultrasonography.
  • Treatment: surgery, medical dissolution.
  • Prognosis: depends on urolith type.
    Print off the owner factsheet on Bladder stones and kidney stones Bladder and kidney stones to give to your client.



Calcium oxalate

  • Crystals: Urinalysis: calcium oxalate crystal ; Uroliths: Urinalysis: calcium oxalate urolith .
  • Acid or neutral urine.
  • Hypercalcemia Hypercalcemia: overview /hypercalciuria, idiopathic hypercalcemia, glucocorticoid excess, vitamin D toxicity Vitamin D poisoning (cholecalciferol), neoplasia).
  • Hyperoxaluria (end product of metabolism of ascorbic acid and amino acids glycine and serine, rare).

Calcium phosphate

Magnesium ammonium phosphate (struvite)

  • Crystals: Stones: Urinalysis: struvite stone .
  • Alkaline urine.
  • Can be associated with urinary tract infection Cystitis: bacterial, especially with urease-producing bacteria.
    This is less common in cats than dogs.


  • Very rare.
  • Severe hepatic dysfunction, eg portosystemic vascular anomaly.

Dried solidified blood calculi

  • Uncommon, possibly the result of chronic inflammation.

Predisposing factors


  • Urinary tract infection (increased risk of struvite).
  • Urine acidifiers (increased risk of calcium oxalate).
  • Magnesium restricted diets (increased risk of calcium oxalate).


  • A nephrolith comprises both mineral and organic components, the mineral component varying greatly and determined by underlying etiology.
  • Supersaturated urine (calculogenic crystalloids)   →   influenced by pH   →   calculi forms   →   grows if able to remain in lumen of excretory pathway of urinary system (urinary stasis).
  • Urine = water + excretory products.
  • Increased concentration of dissolved substance   →   increased precipitation of solid material.
  • Contributing factors: prolonged supersaturation, concentration of other solutes, pH, absence of inhibitors, presence of a nidus (eg urinary tract infection, blood clot), prolonged urinary transit time.


  • Can form in 2-8 weeks.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Palm C & Westropp J (2011) Cats and calcium oxalate: strategies for managing lower and upper tract stone disease. J Fel Med Surg 13 (9), 651-660 PubMed.
  • Barteges J W & Kirk C A (2006) Nutrition and lower urinary tract disease in cats. Vet Clin North Am Small Anim Pract 36 (6), 1361-1376 PubMed.
  • Westropp J L, Ruby A L, Bailiff N L et al (2006) Dried solidified blood calculi in the urinary tract of cats. J Vet Intern Med 20 (4), 828-834 PubMed.
  • Kyles A E, Hardie E M, Wooden B G et al (2005) Management and outcome of cats with ureteral calculi: 153 cases (1984-2002). JAVMA 226 (6), 937-944 PubMed.

Other sources of information

  • BSAVA Manual of Canine and Feline Nephrology and Urology (2007) Elliott J & Grauer G.