We thank Martucci et al. for their letter and their insightful remarks on our article. Their comments highlight the importance of a close collaboration between anesthesiologist-intensivists and hemostasis specialists, as well as a shared understanding of laboratory coagulation tests. They also provide us with the opportunity to clarify the critical issue of measuring anti-Xa levels.

Indeed, not all anti-Xa assays are equivalent. One point is that most of them, but not all, contain dextran sulfate, the characteristics and concentration of which may vary by manufacturer. The intended use of added dextran sulfate is to displace unfractionated heparin from platelet factor 4 released in the blood collection tube by platelets, i.e., to recover circulating active unfractionated heparin. However, this may not always be fully effective. To our knowledge, the clinical impact of choosing one anti-Xa reagent over another has not been evaluated, and this requires well-designed studies....

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