What are the factors that complicate the monitoring of low molecular weight heparin (LMWH) in the treatment of hereditary and acquired hypercoagulability?

Updated: Jan 05, 2018
  • Author: Paul Schick, MD; Chief Editor: Srikanth Nagalla, MBBS, MS, FACP  more...
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In practice, monitoring of LMWH is complicated by several factors. [44] The formulations available for clinical use vary in their composition and relative amounts of anti–factor IIa and anti–factor Xa activity. The optimal anti–factor Xa levels vary among these preparations. Thus, the physician must understand the characteristics of the LMWH being prescribed. [45]

The peak plasma concentrations are achieved at periods of about 4 hours following subcutaneous administration, and this is the time at which blood is usually drawn for monitoring. However, because of different dosage regimens (once or twice daily) and the possibility of different clearance rates, there is no perfect method for the optimum timing of monitoring or determination of desired target levels. [46]

Moreover, standardization of the chromogenic assay for anti–factor Xa activity from different providers and in different laboratories is not yet ideal. [29] Although high doses of LMWH are considered to pose a greater risk of bleeding, no correlation has been shown between anti–factor Xa activity levels and actual incidence of bleeding in patients. Likewise, the assay has limited predictive value for predicting antithrombotic efficiency.

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