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Comparison of prothrombinase-based APC resistance assay and FV Leiden genotyping

Factor V Leiden (FV Leiden) is one of the most common thrombofilic risk factors in general population. Nowdays, when laboratory management is under strong pressure to reduce the number and costs of analysis, the goal is to find out a reliable functional assay that can serve as first-line screening for FV Leiden. The Pefakit APC-R Factor V Leiden (Pentapharm Ltd, Basel, Switzerland) is a functional assay designed to detect activated protein C resistance phenotype (APCR) mostly due to FV Leiden. In contrast to more commonly used APTT-based assays, this is a prothrombinase-based assay, exclusively measuring the susceptibility of plasma FVa to APC-mediated inactivation. The aim of this study was to evaluate the analytical performance of the Pefakit APC-R Factor V Leiden assay in order to find out the sensitivity and specificity of the assay in comparison to DNA analysis. We analyzed 158 patient plasma samples reffered to our laboratory for thrombophilia work- up. By DNA analysis we identified 100 non- carriers, 54 heterozygous and 4 homozygous patients for FV Leiden. The original manufacturer APCR assay was adapted for the Behring Coagulation System analyzer (Siemens Medical Solutions Diagnostics, Germany) and results were expressed as APC ratios. The obtained mean APCR ratios were: 4.04 (range 2.19-5.70) for FV Leiden non-carriers and 1.59 (range 1.30-2.00) for heterozygotes. The same APC ratio of 1.00 was obtained for all 4 homozygotes. The analyzer and assay specific cut- off value of 2.00, obtained by ROC curve analysis, provided 100% sensitivity and 100% specificity, with clear discrimination between non-carriers, heterozygotes and homozygotes. In conclusion, Pefakit APC-R Factor V Leiden assay showed an excellent performance in reliable and accurate distinguishing between FV Leiden carriers and non-carriers.

Factor V Leiden ; APC resistance ; coagulation assay

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