title: Non-infectious phosphate renal calculi: fine structure, chemical and phase composition.
abstract: BACKGROUND
  Chemical composition of internally non-homogeneous phosphate stones should be related to the conditions prevailing during the formation of each individual part.
  
  
  OBJECTIVE
  The object of this paper was to provide a detailed study of phosphate stone composition on the micro- and macro-scales.
  
  
  METHODS
  Fine inner structure, chemical and phase composition of 10 phosphate calculi from different patients were determined by chemical (wet) analysis, observation by scanning microscope, semi-quantitative determination of Ca, Mg, P and C by energy dispersive X-ray and by X-ray diffraction. Results. Eight calculi are formed by amorphous calcium phosphate and two by hydroxyapatite. Magnesium was inversely related to Ca/P ratio. Point chemical composition of solid phase varies in wide limits, i.e. composition of calculus interior is highly inhomogeneous on the microscale. All studied calculi contained an abundance of organic matter incorporated in their volume; the content of carbon was double the calcium content in molar quantities.
  
  
  CONCLUSIONS
  Phosphate renal calculi with the low Ca/P molar ratio predominantly consist of amorphous calcium phosphate whereas those with a high Ca/P molar ratio are composed of poorly crystalline hydroxyapatite which can be partially carbonated. Magnesium may be an inhibitor of HAP formation from urine. Abundant organic matter incorporated into the calculus volume indicates its decisive role at stone formation. Variable point composition of stones implies widely varying conditions during their development.
authors.affiliation: Laboratory of Renal Lithiasis Research, University Institute of Health Sciences Research (IUNICS), University of Balearic Islands, Palma de Mallorca, Spain. fgrases@uib.es
authors.forename: Felix
authors.initials: F
authors.lastname: Grases
authors.forename: Antonia
authors.initials: A
authors.lastname: Costa-Bauza
authors.forename: Rafael M
authors.initials: RM
authors.lastname: Prieto
authors.forename: Isabel
authors.initials: I
authors.lastname: Gomila
authors.forename: Enrique
authors.initials: E
authors.lastname: Pieras
authors.forename: Otakar
authors.initials: O
authors.lastname: Söhnel
mesh_terms: D000328:Adult; D000368:Aged; D017886:Durapatite / Q000737:chemistry*; D005260:Female; D006801:Humans; D007669:Kidney Calculi / Q000737:chemistry / Q000648:ultrastructure*; D008274:Magnesium / Q000737:chemistry; D008297:Male; D008875:Middle Aged; D013052:Spectrometry, X-Ray Emission; D014961:X-Ray Diffraction
chemical_list: D017886:Durapatite; D008274:Magnesium