Novel assay based on diluted prothrombin time reflects anticoagulant effects of direct oral factor Xa inhibitors: Results of multicenter study in Japan.

Background: Direct oral anticoagulants targeting factor Xa (DXaIs) are administered as prophylaxis for various venothrombotic diseases without routine monitoring required. However, assessment of their anticoagulant effects is necessary to prevent severe events, including major bleeding and/or refractory thrombosis.

Objectives: We examined the correlation of ratio of inhibited thrombin generation (RITG), determined using a novel assay based on dilute prothrombin time (dPT), with coagulant markers and laboratory test results to show drug effects. In addition, RITG usefulness as a confirmation test for DXaI therapy was investigated.

Methods: Citrated plasma samples were obtained from patients treated with rivaroxaban (n = 882), apixaban (n = 1214), or edoxaban (n = 820) at 4 different institutions in Japan. Laboratory tests, including prothrombin time (PT), activated partial thromboplastin time (APTT), D-dimer, and plasma concentrations of DXaIs, were conducted, with drug concentrations divided into peak and trough groups, within and after 5 h of administration.

Results: In each DXaI group, RITG was positively correlated with PT, APTT, and drug concentration, and negatively with D-dimer. RITG fluctuation during the peak and trough periods reflected the anticoagulant activity characteristic of each DXaI, which was different from blood concentration fluctuations. RITG showed a significant decrease in cases with thrombosis, while that was increased in those with hemorrhage.

Conclusion: We developed RITG, a novel measurement method based on dPT. RITG represents residual coagulation ability in plasma samples, and is useful for assessment of bleeding and thrombotic tendencies in DXaI patients. RITG can be utilized to confirm the effectiveness of oral anticoagulation therapy with DXaI agents.