Struvite uroliths, also referred to as calculi, are stones within the urinary tract composed of the mineral struvite (also called magnesium ammonium phosphate hexahydrate). Although seen in all ages, struvite urolithiasis is most common in young adult cats. Females are more commonly affected than males. Clinical symptoms depend on the size and number of uroliths as well as their location within the urinary tract. Some affected cats may have no clinical symptoms.
Sterile (non-infected) struvite calculi may be associated with diets high in minerals or diets that lead to alkaline urine. However, in most cases, the cause of struvite urolithiasis in cats remains unknown.
What to Watch For Passage of small volumes of urine
Increased frequency of urination
Inability to urinate may be seen in cats with urethral obstruction (usually males). Affected cats may be extremely ill if they have associated kidney failure or infection.
Routinely performed tests include a complete blood count (CBC), biochemical profile and urinalysis in all cats with struvite calculi. Although often within normal limits, changes consistent with kidney failure or urinary tract infection may be observed. Struvite crystals may be present in the urine, however they are not present in all cases. The absence of struvite crystals in the urine does not rule out struvite urolithiasis. Furthermore, struvite crystals may be observed in the urine of cats that do not have struvite urolithiasis. Bacterial urine culture should be performed because (although uncommon in cats) infection can be associated with struvite calculi.
Additional tests include:
Abdominal radiographs (X-rays) readily identify most struvite calculi. The calculi are dense and appear as white objects in the region of the urinary bladder.
A contrast cystourethrogram (a dye study of the lower urinary tract) or abdominal ultrasonography may help determine the precise size, location, and number of uroliths; however, in most cases, these specialized studies are not necessary.
Depending on the size and location of stones, treatment may be surgical or medical. If the patient is obstructed (blocked), or is having severe clinical signs associated with the presence of stones, surgical removal is necessary. Antibiotic therapy in cats with concurrent bacterial urinary tract infection (uncommon)
Dissolving the stones medically may be effective in some cases. A combination of dietary manipulation and urine acidifying drugs (drugs that increase the acidity of the urine) may be of benefit as these treatments create an environment that discourages struvite formation and facilitates dissolution of existing struvite crystals and stones. An acidifying diet that is low in magnesium and phosphorus and high in salt is fed.
Other treatments include:
Fluid therapy in patients that are dehydrated, have urinary obstruction, or have complicating kidney disease
Urohydropulsion (flushing sterile saline through a catheter in order to move stones out of the bladder) in some female cats or in cats with very small stones (less than 5 mm in diameter) in their bladders.
Home Care and Prevention
Restrict access to other food and treats when dietary management is instituted. Administer all medications and return for follow-up visits as directed by your veterinarian. Feeding your cat an acidifying diet that is magnesium and phosphate restricted may help prevent struvite stone formation.