Methods and apparatus are disclosed for determining 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. The inventive methods and apparatus provide an International Normalization Ratio (INR) based on a coagulation reaction with a blood sample of a living being. Embodiments include methods and apparatus for determining an anticoagulant therapy factor without requiring use of a mean normal prothrombin time determination or an ISI, and may be carried out with the patient sample and a coagulation reagent, where the coagulation reagent may be selected from a number of coagulation reagents. One embodiment provides an INRs value which is determined from a prothrombin time (PT or T1) of a patient blood sample and a theoretical end of test time (TEOT), where a theoretical clotting area is used to determine the INRs value according to the expression, INRs=T1*TEOT*MUL, where MUL is a multiplier that takes into account pixel parity and sampling times. The INRs may be used to determine a course of treatment for a patient or other living being without regard to the specific coagulation regent used to generate the coagulation data (e.g., time and optical activity values).
