Most of us have maintained separate calibration (reference) curves for our chromogenic anti-Xa heparin assays, one each for standard unfractionated heparin (UFH) and low molecular weight heparin (LMWH, enoxaparin, Lovenox), and more recently, the synthetic pentasaccharide, fondaparinux (fonda, Arixtra).
Frequent contributor (friend and colleague) Dave McGlasson (Wilford Hall USAF Medical Center) has published two articles on the use of a hybrid curve that may be used for either UFH or LMWH, thus eliminating the need to inquire which formulation we are testing, and some have even extended the curve mathematically to use it for monitoring fonda. Here are the reference to Dave’s articles:
McGlasson DL. Monitoring unfractionated heparin and low molecular weight heparin anticoagulation with an anti-Xa chromogenic assay using a single calibration curve. Lab Medicine 2005;36:297–9.
McGlasson DL et al: Effects of pre-analytical variables on the anti-FXa chromogenic assay when monitoring unfractionated heparin and Low molecular weight heparin anticoagulation. Blood Coagulation and Fibrinolysis 2005;16:173–6.
At least two hemostasis assay distributors, Aniara and Stago, now make hybrid curve calibrators and advocate for this approach to heparin monitoring, however an informal poll at the recent Thrombosis and Hemostasis Summit of North America in Chicago reveals that most of us are still using individual curves. Consequently, our next quick question (admittedly another unscientific poll), asks us which approach we are taking. Please watch for, and respond to the question. Geo.