Department of Laboratory Medicine
University of Washington
 
Clinical assay interference and limitations

Heparin Activity (anti-Xa activity) [HEPACT]

Methodology: Stago Stachrom Heparin Activity assay

Samples that are drawn through a heparinized line may be contaminated by the heparin in the line. Results of this sample would reflect the anti-Xa activity of the heparin in the patient as well as the heparin in the line and may be erroneously increased.

Samples containing platelet clumps or hemolysis due to difficult blood draws may show decreased heparin activity due to in vitro platelet activation. If results are unexpectedly low redraw the sample and repeat the test.

Unfractionated Heparin (Standard Heparin)

Therapeutic Heparin Activity (anti-Xa units): 0.3 to 0.7 U/mL

Low Molecular Weight Heparin (Enoxaparin)

Measure 4 hours after the last dose

Treatment of DVT, therapeutic Heparin Activity (anti-Xa units)
Twice daily subcutaneous dosing: 0.5 to 1.0 U/mL
Once daily subcutaneous dosing: 1.0 to 2.0 U/mL

Prophylaxis of Thrombosis
Prophylactic Heparin Activity (anti-Xa units): 0.4 to 0.6 U/mL
Prophylaxis in Pregnancy (anti-Xa units): 0.2 to 0.4 U/mL
Prophylaxis in Newborns (anti-Xa units): 0.5 to 1.0 U/mL

Suggested populations to monitor LMW Heparin: renal insufficiency, pregnancy, newborns, markedly obese or underweight patients (pharmacokinetic differences), patients on prolonged therapeutic doses (malignancy, APA, refractory or failed warfarin) to prevent excessive or insufficient anticoagulation

Contact the Coagulation Lab at 206-598-6242 for questions.

References:
Arch Pathol Lab Med 1998;122:799
Stago Stachrom Heparin Activity Assay Package insert, 24524 ­ Revised July 1996




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Created: February 28, 2002
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