The fourth edition of the AMA Guides to the Evaluation of Permanent Impairment (AMA Guides) devoted only a single page to the rating of thrombotic and hemorrhagic disorders, based primarily on analogous impairments from other organ systems and impairments in the activities of daily living (ADLs). The AMA Guides, Fifth Edition, rated thrombotic disorders by the effects on the organ system; criteria for rating hemorrhagic and platelet disorders were based on the treatment required and interferences in ADLs. The sixth edition introduced significant changes, among which are the following: The ratings for hematological disorders were deliberately reduced, especially the highest ratings, because of the inevitable involvement of other organ systems. The goal is for evaluators to rate each organ system based on its defined criteria rather than combining multiple organ system difficulties into a single organ system rating. Also in the AMA Guides, Sixth Edition, separate tables are used to rate hemorrhagic conditions caused by platelet disorders, hemophilia, and clotting disorders. Further, major changes were required because of global methodological changes in this edition, including a significant expansion of the methodology used in rating clotting defects. Finally, the rating for the use of warfarin was altered, and thrombotic disorders are rated using the specific coagulation defect.