Ammonium magnesium phosphate stones (struvite) tend to occur when the urine pH is alkaline and phosphate excretion is high.


Risk Factors:

(1) usually occur in adult women (especially if pregnant) or young males (up to 5 years of age)

(2) presence of a urinary tract infection with urea-splitting bacteria (Proteus, Klebsiella, Providentia, Pseudomonas, Serratia, Staphylococcus, Corynebacterium urealyticum)

(3) high urinary phosphate excretion (typically associated with a high dietary intake)

(4) concentrated urine due to low fluid intake relative to fluid losses

(5) family history of lithiasis

(6) recent history of urological procedure


Sources of dietary phosphate (may affect vegetarians and meat eaters):

(1) cheese

(2) legumes (beans, soy beans, peanuts, etc)

(3) nuts

(4) cocoa

(5) liver

(6) meat


Clinical findings:

(1) presence of renal colic during passage of stones

(2) signs of a urinary tract infection

(3) presence of a staghorn calculus


Laboratory features:

(1) urine with an alkaline pH (> 6.2, may be > 7)

(2) signs of a urinary tract infection (hematuria, nitrates, etc.)

(3) urine sediment shows rectangular crystals resembling "coffin-cover"

(4) often mixed with calcium apatite stones


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