Anti-Factor Xa Activity


  • Monitoring of Enoxaparin (Lovenox) Therapy Under Special Circumstances
  • Monitoring of Factor Xa Inhibitors (Apixaban, Edoxaban, Rivaroxaban) Under Special Circumstances (see Factor Xa Inhibitors, [[Factor Xa Inhibitors]])
  • Monitoring of Fondaparinux (Arixtra) Therapy Under Special Circumstances (see Fondaparinux, [[Fondaparinux]])
  • Monitoring of Unfractionated Heparin Therapy in Patients with a Baseline Prolonged PTT (see Heparin, [[Heparin]])
    • Baseline Prolonged PTT May Be Due to Lupus Anticoagulant, Liver Disease, or an Acquired Factor Inhibitor


  • Anti-Factor Xa Activity is a Functional Assay Utilized to Assess the Degree of Anticoagulation on Certain Anticoagulants
    • Addition of Patient Plasma to Reagent Factor Xa with Measurement of Factor Xa Activity Using an Artificial Factor Xa Substrate in a Chromogenic Assay
    • Factor Xa Activity is Inversely Proportional to the Amount of Heparin (or Other Factor Xa Inhibitor) in the Plasma
    • Due to Differences in Techniques, Target Anti-Factor Xa Levels May Differ Between Laboratories

Timing of Assay Relative to Anticoagulant Dosing

  • Enoxaparin (Lovenox): measure anti-factor Xa activity level 4 hrs after the dose is administered
  • Unfractionated Heparin: measure anti-factor Xa activity level at any time (random level)


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