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.
Keywords: Darapladib; Lp-PLA2; assay validation; cardiovascular disease; reference intervals.