On average, patients taking oral anticoagulants (OAC) in the community are therapeutic only 55% of the time. Anticoagulation control strongly influences the risk of hemorrhagic and thromboembolic events in such patients. However, not all anticoagulation-associated events are attributable to poor anticoagulation control nor do all hemorrhagic or thromboembolic events occur in anticoagulated patients. The objective of this study was to measure the proportion of serious hemorrhagic and thromboembolic events that would be avoided if anticoagulation control was perfect.
This project was a retrospective cohort study of Eastern Ontario using population-based administrative databases. Anticoagulation control was determined for each day of OAC exposure using linear interpolation. Incident hemorrhagic or thromboembolic hospitalizations for control and OAC patients were identified. Hemorrhages and thromboemboli in OAC people were deemed avoidable if they occurred at INRs above three and below two, respectively.
The study included more than 183,000 patient years of observation with 6,400 patient years of OAC exposure. Anticoagulation control could be determined for 51.5% of OAC exposure time. Control patients had hemorrhagic and thromboembolic event rates of 1.8%/yr and 1.5%/yr, respectively. Ten thousand and twenty people were exposed to OAC and spent 14.2% and 26.7% of time with excessively high and low anticoagulation intensity, respectively. Excessively high anticoagulation intensity explained 25.6% (95%CI 19.4-31.7) and 2.0% (95% CI 1.5-2.5) of all serious hemorrhages in the anticoagulated and entire population, respectively. Excessively low anticoagulation intensity explained 11.1% (95%CI 4.4-17.7) and 1.1% (95% CI 0.7-1.6) of all thromboemboli.
This study shows that extreme anticoagulation intensity significantly impacted the health of the population. Improving anticoagulation control will have significant effects on the incidence of serious hemorrhagic and thromboembolic events in the both the anticoagulated and entire population.