title: Crystalluria: prevalence, different types of crystals and the role of infrared spectroscopy.
abstract: BACKGROUND
  Studies on the frequency of the different types of urinary crystals and the role of Fourier transform infrared microspectroscopy (FTIRM) for identification are few. We describe the results of a retrospective study on the prevalence and typology of crystalluria and on the role of FTIRM.
  
  
  METHODS
  Urinary crystals were identified using the combined knowledge of crystal morphology, birefringence features and urine pH (combined approach). When this was inconclusive, FTIRM was performed.
  
  
  RESULTS
  Crystalluria was found in 807 out of 9834 samples (8.2%). In 793, the combined approach identified "typical" crystals, while in 14 FTIRM was needed to identify "atypical" crystals. Among "typical crystals", calcium oxalate (75.9%), uric acid (25.9%) and amorphous urates (7.9%), alone or in combination, were the most frequent. Brushite, ammonium biurate and cystine were the most rare (0.1%-0.7%). FTIRM identified 12 of 14 atypical crystals: three crystals were due to a drug (amoxicillin, indinavir, doubtful phenytoloxamine); four were due to calcium oxalate mono- or bihydrate, uric acid bihydrate or struvite; five were due to calcium carbonate, Tamm-Horsfall glycoprotein, or rare salt combinations.
  
  
  CONCLUSIONS
  Crystalluria is not rare and most crystals can be identified by the combined approach. Occasionally, identification of crystals will require FTIRM.
authors.affiliation: Research Laboratory on Urine, Unità Operativa di Nefrologia, Dialisi, Trapianto, Fondazione IRCCS Ca' Granda, Ospedale Maggiore-Policlinico, Milano, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Verdesca
authors.forename: Giovanni B
authors.initials: GB
authors.lastname: Fogazzi
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Garigali
authors.forename: Piergiorgio
authors.initials: P
authors.lastname: Messa
authors.forename: Michel
authors.initials: M
authors.lastname: Daudon
mesh_terms: D002129:Calcium Oxalate / Q000737:chemistry* / Q000652:urine; D003430:Cross-Sectional Studies; D003460:Crystallization; D006801:Humans; D012189:Retrospective Studies; D017550:Spectroscopy, Fourier Transform Infrared; D014527:Uric Acid / Q000737:chemistry* / Q000652:urine
chemical_list: D002129:Calcium Oxalate; D014527:Uric Acid