title: External quality assessment scheme for biological monitoring of occupational exposure to toxic chemicals.
abstract: OBJECTIVE
  In this study, we summarized the External Quality Assessment Scheme (EQAS) for the biological monitoring of occupational exposure to toxic chemicals which started in 1995 and continued until a 31(st) round robin in the spring of 2010. The program was performed twice per year until 2009, and this was changed to once a year since 2010. The objective of the program is to ensure the reliability of the data related to biological monitoring from analytical laboratories.
  
  
  METHODS
  One hundred and eighteen laboratories participated in the 31(st) round robin. The program offers 5 items for inorganic analysis: lead in blood, cadmium in blood, manganese in blood, cadmium in urine, and mercury in urine. It also offers 10 items for organic analysis, including hippuric acid, methylhippuric acid, mandelic acid, phenylglyoxylic acid, N-methylformamide, N-methylacetamide, trichloroacetic acid, total trichloro-compounds, trans,trans-muconic acid, and 2,5-hexanedione in urine. Target values were determined by statistical analysis using consensus values. All the data, such as chromatograms and calibration curves, were reviewed by the committee.
  
  
  RESULTS
  The proficiency rate was below 70% prior to the first round robin and improved to over 90% for common items, such as PbB and HA, while those for other items still remained in the range of 60-90% and need to be improved up to 90%.
  
  
  CONCLUSIONS
  The EQAS has taken a primary role in improving the reliability of analytical data. A total quality assurance scheme is suggested, including the validation of technical documentation for the whole analytical procedure.
authors.affiliation: Occupational Safety and Health Research Institute, Korea Occupational Safety and Health Agency, Incheon, Korea.
authors.forename: Mi-Young
authors.initials: MY
authors.lastname: Lee
authors.forename: Jeong Sun
authors.initials: JS
authors.lastname: Yang
authors.forename: Seong-Kyu
authors.initials: SK
authors.lastname: Kang