Struvite stones account for 15% of renal calculi. They are associated with chronic urinary tract infection (UTI) with gram-negative rods capable of splitting urea into ammonium, which combines with phosphate and magnesium. Usual organisms include Proteus, Pseudomonas, and Klebsiella species. Escherichia coli is not capable of splitting urea and, therefore, is not associated with struvite stones. Urine pH is typically greater than 7.