AMMONIUM ACID URATE CRYSTAL-FORMATION IN ADULT NORTH-AMERICAN STONE-FORMERS

Although ammonium acid urate (AAU) stones are endemic in Asia, pure AA U calculi have almost disappeared from industrialized countries and cl inical pathophysiologic relevance of sporadic stones containing AAU cr ystals is currently unknown, We reviewed 1,396 crystallographic stone analyses performed in our institution over a 10-year period, Prevalenc e of stones containing AAU crystals and predominantly AAU stones were 3.1% and 0.2%, respectively, In more than two thirds of cases, AAU cry stals represented less than 10% of stone crystal composition, No pure AAU stone was found, According to crystalline predominance, 42%, 35%, and 12% of these calculi were uric acid, infectious, and calcium oxala te stones, respectively, AAU crystals were detected as discrete interc rystalline or peripheral deposits in 74.4% of stones. In only one calc ulus was AAU crystals detected in the nucleus, The hospital charts of 37 patients who presented with 43 calculi containing AAU crystals were also reviewed, The mean age was 53.1 +/- 16.6 years, Fifty-seven perc ent of calculi were upper urinary tract stones and 43% were bladder st ones, Upper urinary tract calculi were more frequently uric acid stone s, followed by infectious and calcium oxalate stones. Lower urinary tr act calculi were more frequently infectious stones, followed by uric a cid stones, Upper urinary tract stones were passed spontaneously in 13 patients and removed surgically in nine patients, Nine of these subje cts were idiopathic recurrent stone formers who had passed other calcu li with no trace of AAU crystal, Fifty-seven percent of lower urinary tract stones were associated with documented bladder dysfunction. In c onclusion, although AAU-containing urolithiases are occasionally seen in our population, predominantly or primarily AAU stones are exception al. AAU crystal formation usually appears as a minor and secondary phe nomenon of no primary pathophysiologic relevance in stone formation. ( C) 1997 by the National Kidney Foundation, Inc.