Main Content

Anti-Xa (Unfractionated Heparin and Low Molecular Weight Heparin)

Test Name:Anti-Xa (Unfractionated Heparin and Low Molecular Weight Heparin)
Epic Order Code:LAB5131  
CPT Code:85520  
Specimen(s) Type:Plasma; Full tube required.
Acceptable Container(s):Top is light blue
Testing Schedule:7 days/week at 1 p.m.
Turn Around Time:STAT: NA  
 Routine: 24 hours
Collection Information:No special patient preparation is required. Obtain specimen by standard collection procedures. If only Anti-Xa is being collected, draw 5 mL into a red top tube, discard and then collect the Anti-Xa tube. A full tube is required.
Transport Information:Deliver to lab immediately. All specimens must be signed into the laboratory.
Reference Clients:If unable to deliver to the lab within 1 hour, centrifuge the specimen for 10 minutes at 3500 RPM to ensure platelet poor plasma.Remove plasma from cells, taking care to avoid the WBC/platelet buffy layer and place into a transport tube. Store and transport at room temperature for up to 4 hours. If testing is delayed beyond this, the sample must be stored and transported frozen at -20° C and delivered to lab within 2 weeks.
Causes for Rejection:Improperly labeled, incorrect container, contaminated, insufficient quantity, incorrect/delay in transport, grossly hemolyzed, clotted, under or over-filled tube.
Reference Range:Therapeutic Ranges:
 Low Molecular Weight Heparin:0.6 - 1.0 IU/mL 
 Unfractionated Heparin: 0.3 - 0.7 IU/mL 
 Patients with ATIII deficiencies may have a non-therapeutic or normal APTT with a therapeutic Anti-Xa heparin Assay.
 J. Hirsh, T. Warkentin, S. Shaughnessy, Heparin and Low Molecular Weight Heparin, Chest 2001: 119-64S-94S
Additional Information:Heparin levels are suggested when there are issues of heparin resistance or great fluctuations in the aPTT after a time of heparin adjustment and what should be a steady state. A minimum time would be 4 hours after the last adjustment bolus. A random heparin level would be non-representative of the patient's true steady state status.
 Do not submit specimens drawn before the 4 hour window. Because: (a) The result is meaningless and interpretation is not possible. If interpretation is attempted, it may lead to an erroneous conclusion. (b) The test is expensive and is not indicated in routine Unfractionated Heparin therapy.