title: Sigma metric analysis for performance of creatinine with fresh frozen serum.
abstract: BACKGROUND
  Six sigma provides an objective and quantitative methodology to describe the laboratory testing performance. In this study, we conducted a national trueness verification scheme with fresh frozen serum (FFS) for serum creatinine to evaluate its performance in China.
  
  
  METHODS
  Two different concentration levels of FFS, targeted with reference method, were sent to 98 laboratories in China. Imprecision and bias of the measurement procedure were calculated for each participant to further evaluate the sigma value. Quality goal index (QGI) analysis was used to investigate the reason of unacceptable performance for laboratories with σ < 3.
  
  
  RESULTS
  Our study indicated that the sample with high concentration of creatinine had preferable sigma values. For the enzymatic method, 7.0% (5/71) to 45.1% (32/71) of the laboratories need to improve their measurement procedures (σ < 3). And for the Jaffe method, the percentages were from 11.5% (3/26) to 73.1% (19/26). QGI analysis suggested that most of the laboratories (62.5% for the enzymatic method and 68.4% for the Jaffe method) should make an effort to improve the trueness (QGI > 1.2). Only 3.1-5.3% of the laboratories should improve both of the precision and trueness.
  
  
  CONCLUSIONS
  Sigma metric analysis of the serum creatinine assays is disappointing, which was mainly due to the unacceptable analytical bias according to the QGI analysis. Further effort is needed to enhance the trueness of the creatinine measurement.
authors.affiliation: a Zhejiang Center for Clinical Laboratories , Zhejiang Provincial People's Hospital , Zhejiang , P. R. China.
authors.forename: Fengfeng
authors.initials: F
authors.lastname: Kang
authors.affiliation: b National Center for Clinical Laboratories , Beijing Hospital , Beijing , P. R. China.
authors.forename: Chuanbao
authors.initials: C
authors.lastname: Zhang
authors.affiliation: b National Center for Clinical Laboratories , Beijing Hospital , Beijing , P. R. China.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: b National Center for Clinical Laboratories , Beijing Hospital , Beijing , P. R. China.
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Wang
mesh_terms: D001800:Blood Specimen Collection / Q000379:methods; D002681:China; D003404:Creatinine / Q000097:blood*; D005615:Freezing; D006801:Humans; D007753:Laboratories / Q000592:standards*; D011786:Quality Control; D017749:Total Quality Management
chemical_list: D003404:Creatinine
keywords: Creatinine; bias; fresh frozen serum; quality control; six sigma