Routine Laboratory Monitoring for Low-Molecular-Weight Heparin Prophylaxis in Burns? Not So Fast!

Abstract : We read with interest the report by Lin et al1 on the use of a protocol to follow-up anti-Xa levels and adjust prophylactic dose low-molecular-weight heparin (LMWH)dosing to maintain anti-Xa levels between 0.2 and 0.4 U/ml. We agree with the authors in their belief that current venous thromboembolic prophylaxis dosing in patients with severe burns may be inadequate. Several recent reports in the trauma critical care literature have identified similar discrepancies between dose and the desired level of anti-Xa activity.2,3 However, we are not quite convinced that routine monitoring and titration of our LMWH dose to a specific target are necessarily the correct strategy. Our recent experience with attempting to apply this strategy has quickly reminded us that we must proceed with great caution. A few months ago, we began checking serum anti-Xa levels 4 hours after subcutaneous administration of LMWH in adults with severe burns (greater than 20% TBSA). If serum anti-Xa levels return to a value less than 0.2 U/ml, each dose of LMWH is increased by 10 mg, and the serum anti-Xa level is rechecked the following day. Consistent with the findings by Lin et al, the standard dose of LMWH for prophylaxis did not seem to be adequate in a large number of patients based on a target anti-Xa level. However, of particular concern was one patient specifically whose anti-Xa level never approached 0.2 U/ml despite reaching a dose as high as 90mgtwice daily. This is the recommended therapeutic dose in an otherwise healthy individual weighing 90 kg for the treatment of a newly diagnosed venous thromboembolism! It seems that Lin et al experienced similar issues as 8 of 38 (21%) never reached their goal before discontinuation of therapy. In addition, we would like to point out that although other variables may be at play, both venous thromboembolic events (VTE) in the reported study occurred in patients who achieved an appropriate anti-Xa level.