title: Standardization of high-sensitivity immunoassays for measurement of C-reactive protein; II: Two approaches for assessing commutability of a reference material.
abstract: BACKGROUND
  We evaluated the commutability of a proposed reference material (PRM), with a formulation based on dilution of Certified Reference Material 470 (CRM470), for 24 high-sensitivity C-reactive protein (hsCRP) methods. We also investigated whether calibration by use of PRM was effective in harmonizing results.
  
  
  METHODS
  A set of 40 native clinical samples was measured along with PRM and 3 dilutions of PRM. We used weighted least-squares polynomial regression (WLS/PR) to perform comparisons between all method combinations and to calculate normalized residuals for the PRM. The PRM was considered noncommutable if any of the normalized residuals for a method pair was >2. Correspondence analysis (CA) was used to explore the multidimensional relationships between methods and samples to evaluate if the PRM had properties similar to native clinical samples. Clinical sample results from the methods for which PRM was commutable were recalibrated based on the PRM results, and ANOVA was used to estimate the CVs before and after recalibration.
  
  
  RESULTS
  After omitting data for 9 methods because of poor precision or procedural flaws, we used data from the 15 remaining methods to evaluate commutability. Using both WLS/PR and CA we found that PRM was noncommutable with 1 method. We found modest improvement in total and among-method CVs when PRM was used to harmonize the results from the 14 methods for which it was commutable.
  
  
  CONCLUSIONS
  A PRM with a formulation based on dilution of CRM470 was commutable with native clinical samples for 14 of 15 hsCRP methods that had acceptable precision. For those methods the use of PRM may contribute to improved harmonization of results for native clinical samples.
authors.affiliation: Division of Laboratory Sciences, National Center for Environmental Health, Centers for Disease Control and Prevention, Atlanta, GA 30341-3724, USA. mkimberly@cdc.gov
authors.forename: Mary M
authors.initials: MM
authors.lastname: Kimberly
authors.forename: Samuel P
authors.initials: SP
authors.lastname: Caudill
authors.forename: Hubert W
authors.initials: HW
authors.lastname: Vesper
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Monsell
authors.forename: W Greg
authors.initials: WG
authors.lastname: Miller
authors.forename: Robert
authors.initials: R
authors.lastname: Rej
authors.forename: Nader
authors.initials: N
authors.lastname: Rifai
authors.forename: Francesco
authors.initials: F
authors.lastname: Dati
authors.forename: Gary L
authors.initials: GL
authors.lastname: Myers
mesh_terms: D002097:C-Reactive Protein / Q000032:analysis*; D002138:Calibration; D019963:Clinical Chemistry Tests / Q000379:methods / Q000592:standards; D006801:Humans; D007118:Immunoassay / Q000379:methods / Q000592:standards; D012015:Reference Standards; D012044:Regression Analysis; D012680:Sensitivity and Specificity
chemical_list: D002097:C-Reactive Protein