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 Heparin and Heparin Sigma) on two different instruments (ACL300+ and AMAX CS190) 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 0.21 U/ml, respectively, while for heparin they were 0.52, 0.55 and 0.41 U/ml, respectively. To test for instrument specific effects, IL-Heparin and Stachrom Heparin were repeated on both instruments on 42 patients receiving unfractionated 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 chromogenic anti-Xa methods do not give equivalent anti-Xa levels for the same samples. Moreover, the differences are clinically significant. This is not explained entirely by instrumentation effects. Recommended therapeutic ranges may need to be method and instrument specific.