WARFARIN MONITORING BY AN ANTICOAGULANT-THERAPY FACTOR (ATF)

In a pilot study (1997) using POTENS+, our coagulation instrument, we determined that: (a) an Anticoagulant Therapy Factor (ATF) was compara ble to the International Normalized Ratio (INR) for monitoring warfari n anticoagulant therapy, (b) one could use any of the four thromboplas tins with which the ATF was derived with comparable results, and (c) t he ATF could be proposed to monitor warfarin therapy. The ATF-INR comp arisons correlated well statistically; but when individual ATF-INR com parisons were later studied, there were frequent discrepancies. The pi lot study (1997) was based on hospitalized patients, so almost all pat ients were undergoing induction of warfarin anticoagulation. Since non e of them had taken warfarin for at least six weeks, none of them coul d be considered ''stable'' on warfarin. In the present study, all pati ents were on warfarin therapy for at least six weeks, and the ATF equa tion was modified by multiplying it by the prothrombin ratio (PR) to g ive a corrected ATF (CATF). This CATF was then further modified to ach ieve agreement with the INR by adjusting the linear regression line by means of analytic geometry, so that the CATF - INR regression line no w had a slope of one and passed through the origin. With these changes , the modified ATFs (MATF) and INRs correlated well and were nearly eq ual numerically when using two of the four thromboplastins. Reason for the discrepancies with the other two thromboplastins will be discusse d.