The Anti-Xa Assay: Therapeutic Monitoring of Heparin

The Anti-Xa Assay: Therapeutic Monitoring of Heparin

Advancing Healthcare Webinar Series

John Mitsios, PhD
Senior Clinical Hemostasis Consultant at Siemens Healthineers


Heparin is an anticoagulant used to prevent and treat blood clots in at-risk patients. Heparin exists in two forms- unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH)- both of which considerably accelerate the inactivation of coagulation factor Xa by antithrombin. Heparin assays are often referred to as anti-Xa assays for this reason. The anticoagulant activity of UFH is somewhat unpredictable. Conversely, LMWH anticoagulant activity is more consistent and predictable. Traditional monitoring of UFH has been done using the APPT assay. However, the assay is fought with pre- and post-analytical and analytical variations. Alternative methods may need to be used to monitor the variable and unpredictable nature of UFH. Therefore, close laboratory monitoring to guide dosing adjustments is often needed.1,2

This presentation is designed for laboratorians who are interested in learning more about heparin monitoring and exploring utilization of anti-Xa assays in their institutions.

Dr. John Mitsios, PhD, Senior Clinical Hemostasis Consultant at Siemens Healthineers will help you:

  • Describe the anticoagulant effects of antithrombin
  • Explain the methods used to determine heparin concentration
  • Determine the limitations of the anti-Xa assay
  • Formulate an approach for conversion to utilizing anti-Xa assay for anticoagulant monitoring


Dr. Mitsios graduated from the University of Ioannina, Greece with a PhD in Chemistry. Upon completion of his doctoral thesis, he then went on to complete a post-doctoral fellowship at the University of California, San Diego. Dr. Mitsios then transitioned to the world of Clinical Chemistry and completed a fellowship at Washington University in St. Louis, MO. His primary research interest throughout his education and training has been in coagulation, with an emphasis on platelet function and biology. Dr. Mitsios joined Siemens-Healthineers as a clinical consultant as part of the Scientific and Clinical Affairs team. In addition, Dr. Mitsios has co-authored 20 peer-reviewed articles and 3 book chapters.

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