Modified anticoagulant therapy factor and international normalized ratio in patients in an unstable coagulation state with respect to warfarin therapy

In our pilot study of 1997, an Anticoagulant Therapy Factor (ATF) was formu lated, compared to the International Normalized Ratio (INR) and proposed to replace the INR. Statistically, replacement of the INR was reasonable; but many discrepancies occurred when the results of ATFs and INRs were compare d for individual patients. The study was based on patients undergoing induc tion of warfarin anticoagulant therapy, so they were "unstable" with respec t to warfarin. A 1998 follow-up study by Carroll and Jackson based on patie nts "stable" with respect to warfarin, having taken the drug for at least s ix weeks, was, therefore, undertaken. In this study, the ATF was modified t o an MATF by both multiplying the ATF by the prothrombin ratio (PR) and adj usting the INR-ATF linear regression analysis line by analytic geometry, so that the slope was one and the line passed through the origin. These modif ications achieved both statistical and individual patient concordance betwe en INRs and ATFs. The purpose of the present paper is to apply the techniqu es of the 1998 study to the original 1997 pilot study to see if the reproce ssed data on the "unstable" patients is, in fact, also concordant with resp ect to INRs and ATFs.