Chromogenic Assay: BIOPHEN DiXaI kit is a chromogenic assay for in vitro quantitative measurement of Factor Xa Direct Inhibitors. (DiXaIs), such as Rivaroxaban, on human citrated plasma (or purified milieu), using a manual or automated method. This method is not appropriate for indirect inhibitors such as Fondaparinux or heparins, as it is totally insensitive to these inhibitors and is specific for Rivaroxaban.