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Comparative Coagulation


HEPARIN MONITORING: HEPARIN (anti-Xa) ASSAY FAQs

Heparin Assay Submission FAQs

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Heparin bottles


Heparin Test Interpretation FAQs

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What sample type is required for heparin assays?

Separated citrate plasma (plasma from a blue top tube) is the only valid sample. DO NOT SUBMIT SERUM OR HEPARIN PLASMA. Ship at least 0.5 mL of plasma in an insulated box with cold packs for overnight delivery.  See http://ahdc.vet.cornell.edu/Sects/Coag/samplingoverview.cfm for detailed sampling instructions.

What is the turnaround time and cost for heparin assays?

Heparin assays are performed daily and results reported same day as sample receipt. Refer to the AHDC test/fee list for current pricing.

When should I draw samples for heparin monitoring?

  • Peak heparin (dogs): Sample 3 hours after SQ dosing
  • Peak heparin (cats): Sample 2 hours after SQ dosing
  • Peak heparin (horses): Sample 3 to 4 hours after SQ dosing
  • Trough heparin (all species): Sample for trough heparin levels just before the next scheduled dose.
  • Steady state values: Sample after 24 to 48 hours of starting heparin


What test should I request to monitor unfractionated heparin (UFH)?

Use test code HEP for unfractionated heparin.

 What test should I request to monitor low molecular weight heparins such as dalteparin and enoxaparin?

Use test code LMWHEP for low molecular weight heparins such as dalteparin (Fragmin) and enoxaparin (Lovenox).

How can I use heparin anti-Xa assays to guide anticoagulant therapy?

Heparin anti-Xa assays measure the patient’s circulating levels of heparin based on specific inhibition of Factor X. High anti-Xa activity indicates high heparin anticoagulant effect. Target anti-Xa ranges developed for people can offer guidelines for animals.

What is the target anti-Xa range for unfractionated heparin*?

Therapeutic range (high intensity anticoagulation) = 0.3 to 0.7 Units/mL
Prophylactic range (low intensity anticoagulation) = 0.1 to 0.4 Units/mL
* Ranges are based on human treatment trials 

What is the target anti-Xa range for low molecular weight heparin*?

Therapeutic range (high intensity anticoagulation) = 0.5 to 1.2 Units/mL
Prophylactic range (low intensity anticoagulation) = 0.2 to 0.5 Units/mL
* Ranges are based on human treatment trials 

Are anti-Xa assays the same as Factor X activity assays?

NO. The anti-Xa assay detects heparin in patient plasma based on inhibition of Factor X in an assay reagent.  Factor X assays (Factor X:C or Factor X coagulant activity) measure a patient’s endogenous level of functional Factor X.

Where can I learn more about heparin therapy?

See the Coagulation Lab’s Heparin web page  heparin anticoagulant therapy, assay methodology, veterinary bibliography and external links.