title: Between-assay variability of faecal calprotectin enzyme-linked immunosorbent assay kits.
abstract: BACKGROUND
  Faecal calprotectin (f-Cp), a marker of intestinal inflammation, can be used to distinguish between functional and organic bowel disease. F-Cp, following extraction, is commonly quantified using enzyme-linked immunosorbent assays (ELISAs) but there are no data comparing the different f-Cp assays or sample extraction devices. We, therefore, evaluated and compared the performance of the Immunodiagnostik, Bühlmann and Eurospital f-Cp ELISA assays as well as the Roche, Immunodiagnostik and ScheBo Biotech commercial faecal extraction devices. We also briefly report results from a pilot f-Cp external quality assurance (EQA) scheme.
  
  
  METHODS
  Imprecision, linearity, recovery, drift and limit of quantitation of the f-Cp assays were evaluated and between-assay variability assessed. The three commercial sample extraction devices were compared with the manual weighing method. Four faecal samples were distributed as part of a pilot EQA scheme to 15 laboratories using quantitative ELISA f-Cp assays.
  
  
  RESULTS
  The three f-Cp assays demonstrated adequate intra-/interbatch imprecision, linearity and recovery. The cross-comparison study and EQA data demonstrated that, for the same sample, the Bühlmann assay reports up to 3.8 times higher f-Cp concentrations than the Immunodiagnostik and Eurospital assays. On average, the commercial extraction devices led to a 7.8-28.1% under-recovery of f-Cp in comparison to the manual weighing method.
  
  
  CONCLUSIONS
  Laboratories should be aware of the lack of the assay standardization, as demonstrated by the between-assay variability. A comparison between f-Cp concentrations reported by these assays and clinical markers of disease severity is required in order to determine their diagnostic accuracy. The EQA scheme represents the first available programme for f-Cp.
authors.affiliation: Department of Clinical Chemistry, New Cross Hospital, Wolverhampton, West Midlands WV10 0QP, UK. simonwhitehead@nhs.net
authors.forename: S J
authors.initials: SJ
authors.lastname: Whitehead
authors.forename: J
authors.initials: J
authors.lastname: French
authors.forename: M J
authors.initials: MJ
authors.lastname: Brookes
authors.forename: C
authors.initials: C
authors.lastname: Ford
authors.forename: R
authors.initials: R
authors.lastname: Gama
mesh_terms: D015415:Biomarkers / Q000032:analysis; D002138:Calibration; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods / Q000592:standards*; D005243:Feces / Q000737:chemistry*; D006801:Humans; D015212:Inflammatory Bowel Diseases / Q000175:diagnosis* / Q000276:immunology; D039841:Leukocyte L1 Antigen Complex / Q000032:analysis* / Q000276:immunology; D057230:Limit of Detection; D011786:Quality Control; D015203:Reproducibility of Results
chemical_list: D015415:Biomarkers; D039841:Leukocyte L1 Antigen Complex