Effect of dabigatran on a prothrombinase-based assay for detecting activated protein C resistance: an ex vivo and in vitro study in normal subjects and factor V Leiden carriers.

Background. The aim of this study was to evaluate ex vivo and in vitro interference of a direct factor IIa inhibitor, dabigatran, on a prothrombinase-based assay to detect activated protein C resistance. Materials and methods. An ex vivo study was performed in six heterozygous factor V Leiden carriers and 12 normal subjects without the factor V Leiden mutation who were treated with dabigatran. An in vitro study was also performed considering 12 plasma samples (six from normal subjects and six from heterozygous factor V Leiden carriers) spiked with dabigatran. The dabigatran concentration was evaluated using a diluted thrombin time assay, activated protein C resistance was evaluated using a prothrombinase-based assay. Results. In both the ex vivo and in vitro studies dabigatran interfered significantly with activated protein C resistance ratios observed in normal subjects and in factor V Leiden heterozygous carriers. Discussion. The results reported in this paper seem to confirm that dabigatran is able to interfere with the Penthafarm prothrombinase-based assay used to study activated protein C resistance, significantly increasing observed ratios. This effect appears to be present already at low concentrations of dabigatran (6 ng/mL) and affects both normal subjects and heterozygous carriers of factor V Leiden. In this group of patients, dabigatran, at concentrations in the therapeutic range (100-200 ng/mL), could markedly increase the activated protein C resistance ratio, bringing it up to within the reference range for normal subjects, thus potentially leading to misclassification of patients.