- Test group B: Patients under therapy with oral thrombin inhibitors (dabigatran) (n=440) No control group of patients not treated with a DOAC is required, as patients take either oral direct factor Xa inhibitors (Test group A) or oral thrombin inhibitors (Test group B), never both. Thus, patients in Test group A are negative for oral thrombin inhibitors and can serve as negative control for Test group B, and vice versa.