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Heparin Assay – also known as Anti-Xa (Ten A) Assay

Blood Sciences Test

Please note: Also known as Anti-Xa (Ten A) assay. This is not the same test as a Factor X assay which is a test of haemostasis function.


Sodium citrate tube

Special Instructions

The sample should be taken 3-4 hrs post the dose of heparin and should be sent urgently.

Factors affecting results

As with all coagulation tests the tubes must not be underfilled. Haemolysis should be avoided. Mix the tube by inversion. Do not shake. Samples should be sent without delay,to avoid potential neutralisation of heparin by platelets.

Reference Ranges

Reference range for prophylaxis =              0.2 – 0.4  IU/mL

Reference range for therapeutic doses =    0.5 – 1.0  IU/mL

Test Usage

For monitoring Low Molecular Weight Heparin

Turnaround time

Weekly – contact lab on 2916

Liquid Xa (Heparin) assays are performed on Tuesdays and Fridays only as stated in the Hospitals Anticoagulation Policy. Any requests made outside of this time should be discussed with and authorised by a Consultant Haematologist.


In House

Clinical Advice

Clinical advice is available from the Haematology Medical team (contact RD&E switchboard on 01392 411611)

Specimen Labelling Procedure
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