Urolithiasis refers to the formation of stones (calculi or uroliths) in the urinary tract. Calculi can be found anywhere in the urinary tract, in the kidneys, the ureter or the bladder, but are most common in the bladder.

Calculi form due to oversaturation of the urine with certain minerals. Several factors may contribute to this oversaturation including increased concentrations of specific minerals in the urine, alterations in the pH (acidity or alkalinity), highly concentrated urine, presence or absence of stimulators, and inhibitors of crystal formation.

Several factors can contribute to development of urolithiasis. These include:

Genetic factors like the altered urate metabolism in Dalmatians

Differences in dietary composition and water intake

Underlying metabolic diseases such as high blood calcium concentration arising from overactivity of the parathyroid glands

Congenital problems such as abnormal blood vessel shunting blood around the liver and contributing to urate stone formation, abnormal transport of cystine in the kidney tubules in Newfoundland dogs

Bacterial infections of the urinary tract (struvite stone formation). The cause for stone formation is unknown in many cases.

The various types of calculi are named according their predominant mineral composition. In dogs, calculi composed of the minerals magnesium ammonium phosphate (commonly called struvite) and calcium oxalate are most common. Urate calculi occur less commonly, often in Dalmatians or English bulldogs. Cystine and silica calculi are relatively rare. The different types of calculi must be treated differently. Consequently, it is important for your veterinarian to be able to obtain calculi for chemical analysis.

Certain breeds of dogs are genetically predisposed to specific stone types. These include:

Oxalate stones in Lhasa apsos.

Urate stones in Dalmatians and English bulldogs

Cystine stones in Newfoundlands

Struvite and oxalate stones in miniature schnauzers and bichon frises

The risk of recurrence for urolithiasis is high and ranges from 20 to 50 percent. The pet's symptoms depend upon the number of stones, their location in the urinary tract, the physical characteristics of the stones (smooth or jagged), and the presence of bacterial urinary tract infection.

What to Watch For

Difficult or frequent urination

Urinating in inappropriate locations

Blood in the urine

Symptoms caused by kidney stones include back or abdominal pain or occasionally abnormal odor to the urine if bacterial infection is present. Surprisingly, however, many pets with kidney stones have few or no symptoms.