Discrepancies in the identification of major bleeding events in patients taking warfarin

Excerpt

Background The method by which major bleeding is defined influences the observed rate of bleeding complications. However, there is no standardized definition of major bleeding for patients taking warfarin. The lack of a consensus definition can influence safety data generated by clinical trials and quality outcomes in anticoagulation clinics. Methods A retrospective analysis of bleeding events in patients taking warfarin and managed by the University of Washington Medical Center Anticoagulation Clinic was performed. Events were evaluated against three definitions of major bleeding, including a subjective definition (“bleeding requiring hospitalization”) and two more objective definitions (ISCOAT and ISTH). Bleeding events that met at least one definition were included in the analysis. Level of agreement among the definitions was determined by the kappa statistic. Results Over a 5 year period, 2631 patients taking warfarin representing 3600 patients—years of therapy experienced 705 bleeding events. Of these, 138 events met at least one of the definitions of major bleeding. The level of agreement between the subjective definition and either of the objective definitions was poor, with kappa statistic value −0.134 (95% CI −0.196 to −0.071). The subjective definition underestimated major bleeding events by excluding events that were managed on an outpatient basis. Conclusions Use of a standard objective definition of major bleeding in clinical trials and in clinical practice is warranted to assess drug safety, quality of care, and total costs of care in patients treated with warfarin. …