title: Ion chromatography for the precise analysis of chloride and sodium in sweat for the diagnosis of cystic fibrosis.
abstract: BACKGROUND
  Measurement of chloride in sweat is an essential part of the diagnostic algorithm for cystic fibrosis. The lack in sensitivity and reproducibility of current methods led us to develop an ion chromatography/high-performance liquid chromatography (IC/HPLC) method, suitable for the analysis of both chloride and sodium in small volumes of sweat.
  
  
  METHODS
  Precision, linearity and limit of detection of an in-house developed IC/HPLC method were established. Method comparison between the newly developed IC/HPLC method and the traditional Chlorocounter was performed, and trueness was determined using Passing Bablok method comparison with external quality assurance material (Royal College of Pathologists of Australasia).
  
  
  RESULTS
  Precision and linearity fulfill criteria as established by UK guidelines are comparable with inductively coupled plasma-mass spectrometry methods. Passing Bablok analysis demonstrated excellent correlation between IC/HPLC measurements and external quality assessment target values, for both chloride and sodium. With a limit of quantitation of 0.95 mmol/L, our method is suitable for the analysis of small amounts of sweat and can thus be used in combination with the Macroduct collection system.
  
  
  CONCLUSIONS
  Although a chromatographic application results in a somewhat more expensive test compared to a Chlorocounter test, more accurate measurements are achieved. In addition, simultaneous measurements of sodium concentrations will result in better detection of false positives, less test repeating and thus faster and more accurate and effective diagnosis. The described IC/HPLC method, therefore, provides a precise, relatively cheap and easy-to-handle application for the analysis of both chloride and sodium in sweat.
authors.affiliation: Department of Laboratory Medicine, University Medical Center Groningen, Groningen, The Netherlands j.doorn@umcg.nl.
authors.forename: J
authors.initials: J
authors.lastname: Doorn
authors.affiliation: Department of Laboratory Medicine, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: T T R
authors.initials: TT
authors.lastname: Storteboom
authors.affiliation: Department of Laboratory Medicine, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: A M
authors.initials: AM
authors.lastname: Mulder
authors.affiliation: Department of Laboratory Medicine, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: W H A
authors.initials: WH
authors.lastname: de Jong
authors.affiliation: Department of Pediatric Pulmonology and Allergy, Beatrix Children's Hospital/University Medical Centre Groningen, GRIAC Research Institute, Groningen, The Netherlands.
authors.forename: B L
authors.initials: BL
authors.lastname: Rottier
authors.affiliation: Department of Laboratory Medicine, University Medical Center Groningen, Groningen, The Netherlands.
authors.forename: I P
authors.initials: IP
authors.lastname: Kema
mesh_terms: D002712:Chlorides / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D002852:Chromatography, Ion Exchange / Q000379:methods*; D003550:Cystic Fibrosis / Q000175:diagnosis* / Q000378:metabolism; D006801:Humans; D012964:Sodium / Q000032:analysis*; D013542:Sweat / Q000737:chemistry*
chemical_list: D002712:Chlorides; D012964:Sodium
keywords: Cystic fibrosis; ion chromatography; sweattest