Ammonium urate stones may occur if certain risk factors are present. These stones can only form when the pH is elevated above 6.5.


Key risk factors resulting in an elevated urine pH:

(1) urinary tract infection with urease-splitting bacteria (associated with pH > 7.0 and struvite stones)

(2) decreased urinary phosphate buffer capacity (associated with pH 6.5 - 7.0)


Dietary risk factors:

(1) diet in a developing country low in phosphate (high rice intake, low intake milk and meat)

(2) anorexia nervosa

(3) certain vegetarian diets with low phosphate intake

(4) high dietary intake of purines


Additional risk factors:

(1) laxative abuse

(2) low fluid intake relative to fluid losses


Steps to decrease risk of ammonium urate stones:

(1) balanced diet with adequate phosphate and reduced urate intake

(2) hydration

(3) discontinuation of laxative use

(4) acidify urine

(5) if a urinary tract infection is present, then treat with antibiotics selected based on antibiotic sensitivities


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