Three different chromogenic methods do not give equivalent anti-Xa levels for patients on therapeutic low molecular weight heparin (dalteparin) or unfractionated heparin

In this study we compare three chromogenic methods (IL-Heparin, Stachrom He parin and Heparin Sigma) on two different instruments (ACL300+ and AMAX CS1 90) for patients on dalteparin (n = 41), a low molecular weight heparin or unfractionated heparin (n = 50). For dalteparin the mean anti-Xa levels for IL-Heparin, Stachrom Heparin and Heparin Sigma were 0.27, 0.30 and 0.21U/m l, respectively, while for heparin they were 0.52, 0.55 and 0.41U/ml, respe ctively. To test for instrument specific effects, IL-Heparin and Stachrom H eparin were repeated on both instruments on 42 patients receiving unfractio nated heparin. For IL-Heparin the mean anti-Xa levels on the AMAX CS190 and ACL300+ were 0.51 and 0.59 U/ml, respectively, while for Stachrom Heparin they were 0.55 and 0.67 anti-Xa U/ml. We conclude that different chromogeni c anti-Xa methods do not give equivalent anti-Xa levels for the same sample s. Moreover, the differences are clinically significant. This is not explai ned entirely by instrumentation effects,Recommended therapeutic ranges may need to be method and instrument specific.