Modified anticoagulant therapy factor and international normalized ratio in patients in an unstable coagulation state...

In our pilot study of 1997, an Anticoagulant Therapy Factor (ATF) was formulated, 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 compared for individual patients. The study was based on patients undergoing induction of warfarin anticoagulant therapy, so they were "unstable" with respect to warfarin. A 1998 follow-up study by Carroll and Jackson based on patients "stable" with respect to warfarin, having taken the drug for at least six weeks, was, therefore, undertaken. In this study, the ATF was modified to an MATF by both multiplying the ATF by the prothrombin ratio (PR) and adjusting the INR-ATF linear regression analysis line by analytic geometry, so that the slope was one and the line passed through the origin. These modifications achieved both statistical and individual patient concordance between INRs and ATFs. The purpose of the present paper is to apply the techniques of the 1998 study to the original 1997 pilot study to see if the reprocessed data on the "unstable" patients is, in fact, also concordant with respect to INRs and ATFs.