Performance characteristics of lipoprotein-associated phospholipase A2 activity assay on the Dimension Vista analyser and preliminary study of a healthy Italian population

INTRODUCTION Lipoprotein-associated phospholipase A2 (Lp-PLA2) is a marker of vascular inflammation associated with coronary heart disease and stroke. We evaluated analytical performance of the PLAC® Activity Test on Siemens Dimension Vista® 1500 analyzer and measured Lp-PLA2 activity in Italian adults to establish reference intervals (RIs) and evaluate correlation with circulating lipids and age. MATERIALS AND METHODS The evaluation protocol consisted of precision, linearity, sensitivity, method comparison, substrate depletion ("hook") effect and interference assessment. Inhibitor (Darapladib) effect was also evaluated. Lp-PLA2 activity was measured in 250 healthy donors (123 males, 127 females, aged 18-70 years). Central 95% RIs were established using nonparametric statistics. RESULTS Intra-assay and inter-assay precision showed CVs of 0.6% - 1.4% and 0.9% - 2.0%, respectively. Linearity replicates showed R2 > 0.98. Limit of quantitation was 5.8 U/L (CV = 9.4%). Bland Altman plot showed bias - 0.9, 95% limits of agreement -6.5 - 4.72. Passing-Bablok regression showed excellent correlation (Slope = 1.02, 95% CI: 1.01 to 1.03; Intercept = - 1.86, 95% CI: - 3.08 to - 1.26; R2 = 0.999). No "hook effect" was observed at Lp-PLA2 activities ≤ 1000 U/L. Average Lp-PLA2 activity in 250 healthy donors was 182 ± 44 U/L (mean ± SD). Males showed statistically significant higher activities than females (P < 0.001). RIs were 107 - 265 U/L for males and 84 - 225 U/L for females. Moderate significant correlation (r = 0.29, P < 0.001) was found between Lp-PLA2 activity and total cholesterol. CONCLUSIONS The PLAC® Activity Test shows very good performance characteristics on Dimension Vista® 1500.