Methods and apparatus are disclosed for determining a new anticoagulant therapy factors for monitoring oral anticoagulant therapy to help prevent excessive bleeding or deleterious blood clots that might otherwise occur before, during or after surgery. New anticoagulant therapy factors maybe based upon the time to maximum acceleration from the time of reagent injection (TX) into a plasma sample, Embodiments include methods and apparatus for determining an anticoagulant therapy factor without requiring use of a mean normal prothrombin time determination or ISI, and may be carried out with the patient sample and a coagulation reagent.