We appreciate the opportunity to respond to issues raised by Dr. Shojania. We agree that the therapeutic anti-Xa heparin level range for LMWH has not been rigorously evaluated; however, the high residual anti-Xa heparin activity observed in our study is a cause for concern because it may increase bleeding during surgery. We believe that when physicians stop warfarin therapy before surgery, they do not intend to substitute another anticoagulant during the surgical procedure.

The difference in mean anti-Xa heparin levels between our study and the study by Ferreira and colleagues (1) is not surprising because their patient population was younger and, in response to anti-Xa measurements, the enoxaparin dose was adjusted to target anti-Xa heparin levels of 0.5 to 1.0 U/mL. Although the preoperative management outlined by Dr. Shojania sounds reasonable, we are aware of no published cohort studies or clinical trials evaluating the safety of this approach.