Prothrombinase-induced clotting time assay for determination of the anticoagulant effects of unfractionated and low-molecular-weight heparins, fondaparinux, and thrombin inhibitors.

The prothrombinase-induced clotting time assay (PiCT, Pentapharm, Basel, Switzerland) is a clotting assay sensitive to factor Xa and factor IIa inhibitors. It is based on the addition of factor Xa and snake venom RVV-V (Russell viper venom factor V activator) specifically activating factor V and phospholipids to platelet-poor plasma. Following an incubation time, the mixture is recalcified and the clotting time is determined. An almost linear dose-response and high sensitivity of the assay for unfractionated heparin (UFH), low-molecular-weight heparins (LMWHs), r-hirudin, and argatroban was found. Fondaparinux showed a nonlinear dose-response. By using ex vivo samples, the following Pearson correlation coefficients were found: r=0.85 between amidolytic anti-Xa and PiCT for 120 LMWH and 24 control samples; r=0.86 between amidolytic anti-Xa activity and PiCT for 68 UFH and 24 control samples; and r=0.94 between ECT and PiCT for 38 hirudin samples. Thus, PiCT is a promising assay for the monitoring of anticoagulants inhibiting factor Xa and/or factor IIa.