AMMONIUM URATE CALCULI - REVIEW OF 26 CASES

A retrospective review of 2,217 consecutive urinary calculi treated at the Massachusetts General Hospital, Boston, MA revealed that 26 (1.2% ) were composed wholly or partly of ammonium urate. Two populations of ammonium urate calculi were identified: Type A or ''septic'' stones ( 15/26) occurred in patients with chronic urinary tract infection, and the ammonium urate was combined with struvite/apatite. Five of 15 were radiolucent and 6/15 also had proven laxative abuse, dietary or bowel disorders. Type B or ''aseptic'' stones (11/26) occurred in patients with ''sterile'' urine; 4/11 were pure ammonium urate, 5/11 were combi ned with calcium oxalate and 2/11 were associated with uric acid or ap atite with no evidence of struvite: 9/11 had a proven history of eithe r laxative abuse, dietary or bowel disorders; 2/11 were radiolucent. ' 'Aseptic'' or ''septic'' ammonium urate calculi may be associated with laxative abuse or other gastrointestinal disorders. All patients with ammonium urate calculi should be questioned regarding laxative overus e and if denied, undergo a spot urine test for Phenolphthalein. Excess ive urinary uric acid may occur in some patients with ''septic'' ammon ium urate stones. These patients may benefit from treatment with Allop urinol.