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Laboratory Test Directory

Anti-Factor Xa Unfractionated Heparin (Updated)


Name Method Department Units
Anti-Factor Xa Unfract.Heparin Chromogenic assay
Core Lab, Coagulation IU/mL

Specimen Requirements

Platelet poor plasma

Container Type Container Size Specimen Volume

Blue plastic tube (Citrate)

2.7 mL 2.7 mL

Frozen - 2 week(s)


Blue plastic tube (Citrate)

1.8 mL 1.8 mL

Frozen - 2 week(s)

Specimen Preparation

  • Fill tubes to appropriate mark.
  • Mix by gentle inversion immediately after collection
  • Centrifuge within 1 hour, separate plasma and freeze
  • Plasma must be platelet free

Reasons for Rejection

  • Over or under filled tube
  • Clotted specimen
  • Not received within specified time frame
  • Gross hemolysis
  • Wrong collection tube
  • Capillary specimen
  • Specimen collected in glass tube
  • Not centrifuged within time frame


Patient specimens are tested 24/7. For plasma samples being sent from an offsite facility: Centrifuge citrate tubes within one (1) hour of collection according to Lab policy, remove platelet-poor plasma, pool the plasma, aliquot and freeze. Send a minimum of two (2) aliquots of plasma.


To view Recommendations for Monitoring Anticoagulant Therapy click here.

CPT Code

  • 85520