Preincubation in the Prothrombinase-induced Clotting Time test (PiCT) is necessary for in vitro evaluation of fondaparinux and to be avoided for the reversible, direct factor Xa inhibitor, rivaroxaban.

There is no clear consensus about tests in vitro that are suitable for evaluating various factor Xa inhibitors. The availability of reversible and irreversible inhibitors further complicates the application of available assays.