How to Monitor Heparin With Anti-Xa

The laboratory will draw off plasma from your blood sample for testing.

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

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.

Tips & Warnings

• Heparin is not intended to dissolve blood clots but may keep blood clots from growing larger.

• According to an article published in Clinical Chemistry, patients with an Anti-Xa activity of greater than 1 IU/ml are at an increased risk of bleeding.

References

• Mayo Clinic: Heparin (Intravenous Route, Subcutaneous Route)
• Mayo Clinic: Unit Code 80609: Heparin Anti-Xa Assay, Plasma
• Lab Tests Online: The Test
• Haliassosa, Alexander, Helen Melita-Manolis, et. al. Use of Anti-Xa Activity as a Marker for Heparin-Induced Bleeding in Patients with APTT >180 s . Clinical Chemistry. 1997.