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Test Code HEPTP Heparin Anti-Xa, Plasma

Secondary ID


Useful For

Measuring heparin concentration:

-In patients treated with low-molecular-weight heparin preparations

-In the presence of prolonged baseline activated partial thromboplastin time (APTT) (eg, lupus anticoagulant, "contact factor" deficiency, etc)

-When unfractionated heparin dose needed to achieve desired APTT prolongation is unexpectedly higher (>50%) than expected


Not useful for monitoring therapy with the heparinoid "danaparoid"

Method Name

Chromogenic Method

Reporting Name

Heparin Anti-Xa, P

Specimen Type

Plasma Na Cit

Specimen Required

Specimen Type: Platelet-poor plasma

Collection Container/Tube: Light-blue top (3.2% sodium citrate)

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions: Spin down, remove plasma and spin plasma again

Additional Information: Double-centrifuged specimen is critical for accurate results as platelet contamination may cause spurious results.

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time
Plasma Na Cit Frozen (preferred) 14 days
  Ambient  2 hours

Reject Due To


Mild OK; Gross Reject


Mild OK; Gross OK


Mild OK; Gross OK



Clinical Information

Heparins are sulphated glycosaminoglycans that inactivate thrombin, factor Xa, and several other coagulation factors; act by enhancing activity of the plasma coagulation inhibitor, antithrombin III (AT III); and prolong the activated partial thromboplastin time (APTT). The anti-Xa assay is the preferred method for monitoring low-molecular-weight heparin (LMWH) therapy because of reduced sensitivity of APTT. Heparin is absent in normal plasma. The heparin level obtained has to be analyzed taking into account the treatment given to the patient (type of heparin, dosage, administration mode, time of sampling, etc) and the desired therapeutic effect. It is clinically recommended that platelet counts be monitored frequently in patients receiving unfractionated heparin (UFH) or LMWH in order to detect heparin-induced thrombocytopenia (HIT).

Reference Values

Adult Therapeutic Range

UFH therapeutic range: 0.30-0.70 IU/mL

(6 hours following initiation or dose adjustment)

LMWH therapeutic range: 0.50-1.00 IU/mL for twice daily dosing*

LMWH therapeutic range: 1.00-2.00 IU/mL for once daily dosing*

LMWH prophylactic range: 0.10-0.30 IU/mL

(*sample obtained 4-6 hours following subcutaneous injection)


Heparin Anti-Xa assay is used to measure heparin concentrations in patients receiving low-molecular-weight heparin or unfractionated heparin.


Results above the therapeutic range may be supratherapeutic suggesting that the heparin dose may need to be decreased. 

Results below the therapeutic range may be subtherapeutic suggesting that the heparin dose may need to be increased.

Clinical Reference

1. Marci CD, Prager D: A review of the clinical indications for the plasma heparin assay. Am J Clin Pathol 1993;99:546-550

2. Houbouyan L, Boutiere B, Contant G, et al: Validation of analytical hemostasis systems: measurement of anti-Xa activity of low-molecular-weight-heparins. Clin Chem 1996;42:1223-1230

3. Jeske W, Messmore HL Jr, Fareed J: Pharmacology of heparin and oral anticoagulants. In Thrombosis and Hemorrhage. Second edition. Edited by J Loscalzo, AI Schafer. Baltimore, MA, Williams and Wilkins, 1998, pp 1193-1204

4. Monagle P, Michelson AD, Bovill E, Andrew M: Antithrombotic therapy in children. Chest 2001;119:344-370

5. Fraser G, McKenna J: Monitoring low molecular weight heparins with antiXa activity: house of cards or firm foundation? Hospital Pharmacy 2003;38:202-211

6. Nutescu EA, Spinler SA, Wittkowsky A, Dager WE: Low-molecular-weight heparins in renal impairment and obesity: available evidence and clinical practice recommendations across medical and surgical settings. Ann Pharmacother 2009;43:1064:1083

Day(s) and Time(s) Performed

Monday through Sunday; Continuously

Analytic Time

Same day/1 day

Performing Laboratory

Mayo Medical Laboratories in Rochester

Test Classification

This test has been cleared or approved by the U.S. Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
HEPTP Heparin Anti-Xa, P In Process


Result ID Test Result Name Result LOINC Value
HEPTP Heparin Anti-Xa, P In Process