title: Evaluation of recombinant enzyme calibration to harmonize lipoprotein-associated phospholipase A2 activity results between instruments.
abstract: OBJECTIVE
  Enzymatic activity of lipoprotein-associated phospholipase A2 (Lp-PLA2) mediates vascular inflammation in coronary heart disease (CHD). Calibration of Lp-PLA2 activity measurements using a recombinant enzyme was performed to assess intra- and inter-laboratory assay precision and accuracy in routine clinical settings.
  
  
  METHODS
  Test performance assessment included recovery, analytical sensitivity, linear range, within-lab and site-to-site precision, interference, and analyte stability. Results using the Beckman-Coulter AU400 analyzer were compared to other chemistry analyzers.
  
  
  RESULTS
  Lp-PLA2 activity ranged from 84 to 303nmol/min/mL in 300 subjects, with 82.0% and 18.0% measurements below and at or above a cut-point of 225nmol/min/mL, respectively. Results of matched K2-EDTA plasma and serum (n=131) were similar with a slope of 1.00, y-intercept of 0.05, and R-value of 0.988. Mean recovery ranged from 90 to 106% of baseline after storage at different temperatures and time periods. Limit of detection was ≤10nmol/min/mL, without deviation from linearity between 10 and 382nmol/min/mL. Endogenous substances and medications did not interfere with the activity measurements. Overall intra- and inter-laboratory precision among three sites showed coefficients of variation of ≤3.8% and ≤5% respectively. Limit of quantitation was 1.3nmol/min/mL. Method comparison studies for multiple analyzers demonstrated slopes, intercepts or R(2) coefficients ranging from 0.96 to 1.06, -5.6 to 2.0, or 0.997 to 0.999, respectively.
  
  
  CONCLUSIONS
  Analytical performance of the calibrated PLAC(®) test for Lp-PLA2 enzyme activity assay in CHD is resistant to a wide variety of pre-analytical factors, with site-to-site reproducibility on multiple analyzers sufficient to standardize results in diverse laboratory settings.
authors.affiliation: Diadexus, Inc., South San Francisco, CA 94080, United States.
authors.forename: Mary Jane
authors.initials: MJ
authors.lastname: Cerelli
authors.affiliation: Diadexus, Inc., South San Francisco, CA 94080, United States.
authors.forename: Karen
authors.initials: K
authors.lastname: Grimm
authors.affiliation: Diadexus, Inc., South San Francisco, CA 94080, United States.
authors.forename: Xiaozhu
authors.initials: X
authors.lastname: Duan
authors.affiliation: Diadexus, Inc., South San Francisco, CA 94080, United States.
authors.forename: Edie
authors.initials: E
authors.lastname: Mulberg
authors.affiliation: Diadexus, Inc., South San Francisco, CA 94080, United States.
authors.forename: Maria
authors.initials: M
authors.lastname: Jalilie
authors.affiliation: Diadexus, Inc., South San Francisco, CA 94080, United States.
authors.forename: Phillip
authors.initials: P
authors.lastname: Sekella
authors.affiliation: Diadexus, Inc., South San Francisco, CA 94080, United States.
authors.forename: Marta
authors.initials: M
authors.lastname: Payes
authors.affiliation: Diadexus, Inc., South San Francisco, CA 94080, United States.
authors.forename: Heather
authors.initials: H
authors.lastname: Cox
authors.affiliation: University of Oklahoma College of Medicine, Department of Pathology, Oklahoma City, OK 73190, United States.
authors.forename: Kenneth E
authors.initials: KE
authors.lastname: Blick
authors.affiliation: Diadexus, Inc., South San Francisco, CA 94080, United States.
authors.forename: Kenneth C
authors.initials: KC
authors.lastname: Fang
authors.affiliation: Diadexus, Inc., South San Francisco, CA 94080, United States. Electronic address: ezychlinsky@diadexus.com.
authors.forename: Emi
authors.initials: E
authors.lastname: Zychlinsky
mesh_terms: D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase / Q000378:metabolism*; D002138:Calibration; D006801:Humans; D057230:Limit of Detection; D011994:Recombinant Proteins / Q000378:metabolism; D015203:Reproducibility of Results
chemical_list: D011994:Recombinant Proteins; D043203:1-Alkyl-2-acetylglycerophosphocholine Esterase
keywords: Calibration; Cardiovascular disease; Enzyme activity; Lipoprotein-associated phospholipase A(2); Standardization