title: Urolithiasis in Okinawa, Japan: a relatively high prevalence of uric acid stones.
abstract: OBJECTIVE
  The aim of the present study was to investigate the composition of urinary tract stones in patients from Okinawa, the most southern island group of Japan.
  
  
  METHODS
  The study was conducted by 12 hospitals in Okinawa. A total of 1816 urinary tract calculi were obtained from 1816 patients (1323 males; 493 females). The patients had a mean age of 53 +/- 15.3 years (mean +/- SD). The calculi were examined to determine their chemical composition. Stone samples were analyzed by computed infrared spectrophotometer.
  
  
  RESULTS
  Pure stones comprised 58.4% of the total, with calcium oxalate stones accounting for 40% (21% monohydrate [whewellite]; 6.6% dihydrate [weddellite]; and 12.4% combined monohydrate and dihydrate stones), uric acid/urate stones for 9.6%, calcium phosphate stones for 5.1%, and struvite stones for 3.7%. The other 41.6% of the stones consisted of calcium oxalate mixed with other components. The male-to-female ratio was 2.7:1.
  
  
  CONCLUSIONS
  In our series, calcium oxalate stones accounted for 81.6% of the urinary tract calculi, while uric acid/urate stones accounted for 15.8%. Uric acid stones, predominantly the anhydrous and/or dihydrate forms, showed a relatively high prevalence. Calcium oxalate stones, predominantly in the form of whewellite, showed a high prevalence among pure calculi; while the predominant combinations among mixed calculi were weddellite + calcium phosphate and whewellite + uric acid/urate.
authors.affiliation: Department of Urology, Faculty of Medicine, University of the Ryukyus, Nishihara, Okinawa, Japan. k008744@med.u-ryukyu.ac.jp
authors.forename: Rayhan Zubair
authors.initials: RZ
authors.lastname: Hossain
authors.forename: Yoshihide
authors.initials: Y
authors.lastname: Ogawa
authors.forename: Sanehiro
authors.initials: S
authors.lastname: Hokama
authors.forename: Makoto
authors.initials: M
authors.lastname: Morozumi
authors.forename: Tadashi
authors.initials: T
authors.lastname: Hatano
mesh_terms: D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D002129:Calcium Oxalate / Q000378:metabolism; D002130:Calcium Phosphates / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D015994:Incidence; D007564:Japan / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D017678:Sex Distribution; D014527:Uric Acid / Q000378:metabolism*; D014545:Urinary Calculi / Q000737:chemistry* / Q000453:epidemiology*
chemical_list: D002130:Calcium Phosphates; C485828:alpha-tricalcium phosphate; C485830:tetracalcium phosphate; D002129:Calcium Oxalate; D014527:Uric Acid; C485838:calcium phosphate, monobasic, anhydrous; C020243:calcium phosphate; C485829:calcium phosphate, dibasic, anhydrous