How to Monitor Heparin With Anti-Xa

Heparin blocks coagulation factors in the bloodstream and prevents blood clots. Patients receive heparin intravenously or subcutaneously in a hospital setting. Professional staff monitor the patient's blood-clotting factors and heparin levels, taking frequent blood samples that are tested for Anti-Xa activity. Typically this assay is used with low molecular weight heparin (LMWH) not unfractionated heparin (UH), because LMWH has a more consistent particle size. Anti-Xa measures the coagulation binding potential of a blood sample to monitor whether the patient is receiving too much heparin.

Things You'll Need

• Light blue-topped blood vial containing 3.2% sodium nitrate
• Centrifuge
• Plastic vial
• Chromogenic assay machine

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Instructions

Monitoring Heparin Levels Using Anti-Xa Assay

• 1

  Collect a blood sample into a light blue-topped blood vial containing 3.2% or 3.8% sodium nitrate. The sodium nitrate will act as an anti-coagulant. The procedure doesn't permit another anti-coagulant. Professional staff can take samples before or after heparin injections depending on the physician's monitoring requirements.

• 2

  Spin down the blood sample in a centrifuge.

• 3

  Draw off 1mL of plasma and place in a clean vial. The plasma is the clear yellowish liquid at the top of the vial.

• 4

  Spin down the plasma sample in a centrifuge.

• 5

  Draw off the entire plasma sample,being certain to leave any precipitant at the bottom of the vial. Put the plasma in a plastic vial.

• 6

  Insert the sample into a testing machine. The assay is performed using an automated chromogenic testing machine. The Mayo Clinic specifically references the chromogenic method on STA-R Evolution.

• 7

  A laboratory technician and doctor interpret test results. Depending on the Anti-Xa levels, the doctor may increase or decrease the dosage of heparin.