Performance characteristics of an immunoturbidimetric assay for lipoprotein-associated phospholipase A2

Background: Lipoprotein-associated phospholipase A2 (Lp-PLA2) is an inflammatory biomarker for coronary heart disease and ischemic stroke risk assessment. Methods: The Plac® turbidimetric immunoassay (TIA) for measurement of Lp-PLA2 was evaluated for limit of blank, functional sensitivity, dilution linearity, imprecision, interferences, and comparison to an ELISA assay for Lp-PLA2. Results: The assay was linear from 100 to 500 μg/l. Total inter-assay CVs were < 3% for both control levels. Interference studies showed recoveries of 90-110% of expected values at interferent concentrations up to 15 g/l hemoglobin, 450 mg/l bilirubin, and 41 g/l triglycerides. Comparison of 3 sample sets collected using different protocols gave the following regression statistics for the Plac TIA compared to the Plac ELISA: sample set 1 (n = 99) slope = 1.5, intercept = - 122.4, Sy/x = 71.3 μg/l, and r = 0.61; sample set 2 (n = 100) slope = 2.1, intercept = - 173 μg/l, Sy/x = 55 μg/l, and r = 0.82; sample set 3 after 1 freeze-thaw cycle (n = 30) slope = 1.2, intercept = -68.6 μg/l, Sy/x = 28.6 μg/l, and r = 0.82; sample set 3 after a second freeze-thaw cycle slope = 1.4, intercept = - 68.2 μg/l, Sy/x = 33.1 μg/l, and r = 0.83. Conclusions: The Plac TIA reagents perform acceptably on the Roche Modular P analyzer. However, only a fair correlation was observed between the Plac ELISA and Plac TIA assays. © 2009 Elsevier B.V. All rights reserved.