Evaluation of recombinant enzyme calibration to harmonize lipoprotein-associated phospholipase A2 activity results between instruments.

Objectives: 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.

Design And 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.

Conclusion: 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.