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Heparin (Anti-Xa) Assay

Department of Haematology

Notes

  • This test is used to measure absolute levels of heparin in patient plasma.
  • The Anti-Xa assay should only be used to monitor patients on Low Molecular Weight Heparin (LMWH);
    • children
    • pregnancy
    • patients with renal failure
    • patients with extreme body weight.
  • In all other situations the test will only be performed following discussion with the Consultant Haematologist.
  • It is important that the specimen is collected within the correct time frame post heparin administration. Please see table below.
  • The timing is not so critical if the patient is on continuous infusion regime. Note: The test is unvalidated for Unfractionated heparin, therefore caution must be taken with interpreting the result. Discuss with Consultant Haematologist.
  • Performed at GRH. (Please see table below).

Sample Requirements

3.5ml Trisodium Citrate sample

3ml Trisodium citrate

See notes. 2ml (blue cap, white ring) partial draw samples are NOT suitable for anti-Xa assays.

Turnaround Times

Urgent: same day may be possible, please always contact the laboratory in advance.

Routine: within 2 weeks

Reference Ranges

Range Units
Therapeutic dose of Unfractionated Heparin 0.2 - 0.4 iu/ml Heparin
Therapeutic dose of LMWH (eg. Fragmin or Enoxaparin) 0.5 - 1.0 iu/ml Heparin

These therapeutic ranges may be altered for individual patients but this is a clinical decision made by the Consultant Haematologists.

Where Test Are Performed

Drug Alternate Name Where Tested Notes
Clexane Enoxaparin In house (GRH) When used for dosing purpose the sample should be 4 hours post last LMWH dose. Separate and freeze within 2 hours of collection.
Test not available OOH.
Fragmin Dalteparin In house (GRH) When used for dosing purpose the sample should be 4 hours post last LMWH dose. Separate and freeze within 2 hours of collection.
Test not available OOH.
Rivaroxaban Xarelto Sent to reference centre: Oxford Haemophilia Centre Prothrombin time effected.
When used for dosing purpose the sample should be 3-4 hours post last dose to determine peak levels. Separate and freeze within 2 hours of collection.
Test not available at GHNHSFT.
Apixaban Eliquis Sent to reference centre: Oxford Haemophilia Centre Prothrombin time and Activated partial thromboplastin time effected.
When used for dosing purpose the sample should be 3-4 hours post last dose to determine peak levels. Separate and freeze within 2 hours of collection.
Test not available at GHNHSFT.
Danaparoid Orgaran Sent to reference centre: Oxford Haemophilia Centre Test not available at GHNHSFT.
Contact Oxford Haemophilia Centre.
Fondaparinux Arixtra Sent to reference centre: Oxford Haemophilia Centre When used for dosing purpose the sample should be 3 hours post last dose to determine peak levels. Separate and freeze within 2 hours of collection.
Test not available at GHNHSFT
Tinzaparin Innohep In house (GRH) When used for dosing purpose the sample should be 4 hours post last LMWH dose. Separate and freeze within 2 hours of collection.
Test not available OOH.
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