title: Comparison of procedures for evaluating laboratory performance in external quality assessment schemes for lead in blood and aluminum in serum demonstrates the need for common quality specifications.
abstract: BACKGROUND
  The different scoring methods used by eight European External Quality Assessment Schemes (EQASs) for occupational and environmental laboratory medicine were compared to develop suitable quality specifications as a step toward harmonization.
  
  
  METHODS
  Real results for blood lead and serum aluminum assays, reported by participants in Italian and United Kingdom EQASs, were evaluated according to individual scheme scoring criteria. The same results were then used to produce z scores using scheme-based between-laboratory SDs as the estimate of variability to determine whether simple performance-derived quality specifications produced better agreement among schemes.
  
  
  RESULTS
  The schemes gave conflicting assessments of participants' performance, and participants judged to be successful by one scheme could be defined as performing inadequately by another. An approach proposed by Kenny et al. (Scand J Clin Lab Invest 1999;59:585), which uses clinical inputs to set targets for analytical imprecision, bias, and total error allowable, was then used to elaborate quality specifications.
  
  
  CONCLUSIONS
  We suggest that the CLIA '88 recommendations for blood lead (+/- 40 micro g/L or +/- 10% of the target concentration, whichever is the greater) could be used as a quality specification, although a revision to +/- 30 micro g/L or +/- 10% is recommended. For serum aluminum, a suitable quality specification of +/- 5 micro g/L or +/- 20% of the target concentration, whichever is the greater, is suggested. These specifications may be used to compare laboratory performance across schemes.
authors.affiliation: Centre for Clinical Science and Measurement, School of Biomedical and Life Sciences, University of Surrey, Guilford GU2 7XH, United Kingdom. A.Taylor@surrey.ac.uk
authors.forename: Andrew
authors.initials: A
authors.lastname: Taylor
authors.forename: Jurgen
authors.initials: J
authors.lastname: Angerer
authors.forename: Francoise
authors.initials: F
authors.lastname: Claeys
authors.forename: Jesper
authors.initials: J
authors.lastname: Kristiansen
authors.forename: Olav
authors.initials: O
authors.lastname: Mazarrasa
authors.forename: Antonio
authors.initials: A
authors.lastname: Menditto
authors.forename: Marina
authors.initials: M
authors.lastname: Patriarca
authors.forename: Alain
authors.initials: A
authors.lastname: Pineau
authors.forename: Ilse
authors.initials: I
authors.lastname: Schoeters
authors.forename: Christophe
authors.initials: C
authors.lastname: Sykes
authors.forename: Sinikka
authors.initials: S
authors.lastname: Valkonen
authors.forename: Cas
authors.initials: C
authors.lastname: Weykamp
mesh_terms: D000535:Aluminum / Q000097:blood*; D019411:Clinical Laboratory Techniques / Q000592:standards*; D004785:Environmental Pollutants / Q000097:blood* / Q000592:standards; D005062:European Union; D006801:Humans; D007854:Lead / Q000097:blood*; D016273:Occupational Exposure; D011786:Quality Control; D012016:Reference Values
chemical_list: D004785:Environmental Pollutants; D007854:Lead; D000535:Aluminum