Struvite stones comprise about 10–15 % of all kidney stones

They occur more frequently in women in an approximate 2:1 ratio. This is thought to be due to the higher prevalence of urinary tract infections in women.

Presenting signs are not always typical renal colic as in other stone types, but is usually recurrent urinary tract infections and may include the following with their frequency of occurrence:

Production of an infection stone requires urea, water, calcium (Ca), magnesium (Mg), phosphate (PO₄), urine with pH>6.8–7.2, and the urease enzyme.

Bacteria that contain the enzyme, urease, break down urea which results in increasing ammonia and carbon dioxide. Both gram-positive and gram-negative organisms can produce this enzyme.

Carbonate apatite begins to crystallize at urine pH greater than 6.8 and magnesium ammonium phosphate (struvite) crystallizes at pH greater than 7.2.

Struvite stones can be found bilaterally in 15 % of cases.

When the urinary environment is receptive, struvite stones can form rapidly; even within 4–6 weeks [3].

Definitive diagnosis is made by stone analysis of magnesium ammonium phosphate or carbonate apatite.

Microbiological culture of stones is the best source to identify which urease-producing bacteria is responsible, but this is not always detectable. The second best site to identify bacteria is from urine sampled directly from the kidney since it is closest to the site of the infected stone.

Voided urine culture is not always congruent with the underlying urease-producing bacteria responsible for stone formation.

The most common species that possess the urease enzyme are Proteus, Providencia, Serratia ureilytica, and Morganella morganii. Only 1.4 % of Escherichia coli species produce urease.

If urease-producing bacteria are identified on culture, their mere presence does not always result in struvite stone formation. Despite the fact that up to 39 % of UTIs are associated with urease-producing bacteria, the incidence of struvite stones is still only 16 % suggesting that the presence of a urease positive pathogen is not the only criterion and that other factors must be present in order for a struvite stone to form [3].

Urine pH is typically greater than 6.8 (>6.8 produces carbonate apatite stones and once >7.2, struvite stones form).

As with renal calculi in general, a low sodium diet and high water diet may aid in preventing calculi, as well as modifying risk factors for urinary tract infections such as: limiting foreign bodies to urinary tracts, treating constipation, minimizing stasis of urine, and minimizing immune compromised states. High protein diets have been shown to acidify the urine in veterinary studies and reduce struvite crystals [4], but this is not a proven strategy for struvite stone prevention in humans.

Treatment and directed therapy of struvite stones is necessary. Conservative non-surgical management however carries a higher 10-year mortality (28 %) compared to those who are managed surgically with stone extraction (7.2 %) [5]. The rate of renal failure is also higher in those managed non-surgically (36 %) compared to those treated with surgery (15.9 %) [1].

Patients with staghorn calculi who did not undergo surgery were more likely to have renal failure and death (67 %) compared to those who were treated successfully with surgery (0 % mortality) [6]. The same study showed that if infected stone fragments were not entirely cleared, the mortality rate rose from 0 to 2.9 %. Furthermore, the recurrence rate rises to 85 % if residual stone fragments remain.

Three principles are paramount in the treatment of infection stones [3]:

There is no set diet to prevent infection stones, and dietary recommendations should be developed and implemented individually, on a case-by-case basis. Acidification therapy with cranberry juice has been used in veterinary studies with some success, but the dosage required would have to be high enough to reduce urine pH [7–9]. Currently, the use of cranberry juice to prevent infection stones remains theoretical in human populations.