The following article features coverage from the 61st American Society of Hematology Annual Meeting and Exposition. Click here to read more of Hematology Advisor’s conference coverage.

Adding aspirin to treatment with direct-acting oral anticoagulants (DOACs) when the combination is not indicated may increase risk for bleeding, according to research presented at the 61st American Society of Hematology (ASH) Annual Meeting in Orlando, Florida.

Currently, most data surrounding the combination of anticoagulation with aspirin come from patients receiving warfarin and aspirin. To assess the effect of adding aspirin to DOAC treatment, researchers conducted a registry-based cohort study of 2045 patients receiving DOAC therapy to treat venous thromboembolism or nonvalvular atrial fibrillation. The primary outcome was any new bleeding event, and secondary outcomes included arterial or venous thromboembolism, type of bleed, and death.

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Approximately one-third of patients (647 patients) received aspirin in combination with a DOAC without a clear indication. The researchers identified 2 propensity-matched cohorts of 639 patients each who received either DOACs and aspirin or DOAC monotherapy.

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There were 319 bleeding events in the DOAC plus aspirin cohort, compared with 261 bleeding events in the DOAC monotherapy cohort (P =.02), yielding bleed rates per 100 patient-years of 39.50 and 32.32, respectively (P =.07). This difference was primarily due to a higher number of nonmajor bleeds (rate per 100 patient-years, 32.82 vs 25.88; P =.04) and clinically relevant nonmajor bleeds (rate per 100 patient-years, 18.70 vs 13.50; P =.02) in patients receiving combination therapy, as no significant differences were seen for other bleeding types between the patient groups. There were 2 fatal bleeding events reported, both of which occurred in the DOAC monotherapy cohort.

The rate of thrombosis was similar in both groups; patients receiving combination therapy experienced 2.23 new thrombotic events per 100 patient-years while patients receiving DOACs alone experienced 2.35 new thrombotic per 100 patient-years (P =.95). There was a trend toward increased hospitalization and emergency room visits in patients receiving both DOACs and aspirin compared with patients receiving DOACs alone, but this difference was not statistically significant (P =.14).

These findings suggest that combining DOAC treatment with aspirin without an indication for combination therapy may increase risk for bleeding events without decreasing thrombotic incidence. However, “this study is overall small,” cautioned presenter Jordan K Schaefer, MD, of the University of Michigan in Dexter, “and [it is] likely underpowered for the outcome of thrombosis and potentially underpowered for bleeding outcomes as well. These findings need to be confirmed in larger studies. Until such data [are] available, clinicans and patients must balance the relative risks and benefits of adding aspirin to full-dose DOAC therapy.”

Disclosures: Some authors have declared affiliations with the pharmaceutical industry. Please refer to the original study for a full list of disclosures.


  1. Schaefer JK, Li Y, Kong X, et al. Impact of adding aspirin to direct oral anticoagulant therapy without an apparent indication. Oral presentation at: 61st ASH Annual Meeting and Exposition; December 7-10, 2019; Orlando, FL. Abstract 787.