Heparin Anti Xa, Unfractionated Heparin

anti-Factor Xa, anti-Xa assay, Heparin anti Xa, unfractionated , Antrim #26180, EPIC: LAB5192, SOFT: UNFHP


Specimens with hematocrit values greater than 55% must have anticoagulant adjusted. Specimens must be re-collected using a specified whole blood to sodium citrate ratio. Contact the performing Laboratory for specific instructions.

Specimen Collection Criteria

Collect: One Light Blue-top Becton-Dickinson 3.2% Sodium Citrate tube.


Physician Office/Drawsite Specimen Preparation

For optimal results, maintain whole blood specimen at room temperature (20-26°C or 68-78.8°F) prior to transport. Transport whole blood to the Laboratory within 4 hours of collection. If transport within 4 hours is not possible, the following procedure must be followed for accurate results:

  1. Centrifuge the capped tubes at 1500 x g for 15 minutes.
  2. Transfer plasma with plastic pipette into a plastic polypropylene centrifuge tube, cap and centrifuge an additional 15 minutes at 1500 x g to obtain platelet poor plasma (PPP) which has a platelet count less than 10 bil/L. Plasma with a platelet count of less than 10 bil/L is critical for accurate results.
  3. Immediately remove only the top two-thirds of the PPP and transfer into a plastic tube.
  4. Freeze (-20°C/-4°F or below) the PPP immediately.
  5. Transport frozen on DRY ICE. Specimen must remain frozen during transport.  

Preparation for Courier Transport

Transport: Whole blood at room temperature (20-25°C or 68-77°F), or plasma obtained through the process listed above, frozen (-20°C/-4°F or below).

Rejection Criteria

  • Glass tubes and 3.8% Sodium Citrate tubes.
  • Specimens that are clotted or grossly hemolyzed.
  • Inappropriate specimen volume.
  • Thawed or partially thawed specimens. 


Monday - Friday, 7:00 a.m. - 3:30 p.m.
Results available within 24 hours.

Reference Range

Therapeutic Range: 0.3 - 0.7 U/mL.

Test Methodology

Chromogenic (IL ACL TOP Series).


A positive result indicates that some form of heparin is present. Pharmacy Dosing Services provides consultative services and dosage guidelines for anticoagulant management. Refer to Pharmacy Dosing Services located on Inside Beaumont Online>Pharmacy>Beaumont, Royal Oak>Services>Pharmacokinetic Dosing Services>Anticoagulation Dosing Guidelines.

Clinical Utility

Test used to quantitate heparin activity in anti Xa units. For monitoring unfractionated heparin therapy.

CPT Code


Test Codes

Antrim #26180, EPIC: LAB5192, SOFT: UNFHP

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