Activité anti-Xa

Anti-Xa Assay


The examination will test the effectiveness of low molecular weight heparins (LMWH), other conventional tests are not feasible due to low antithrombin activity of LMWHs.


While heparin acts on three factors of coagulation, LMWHs act only on factor Xa, where the principle of the assay of the anti-Xa assay.

Anti-Xa Assay

blood sample taken 3-4 hours after subcutaneous injection of LMWH, at the time of peak plasma concentration of the product.

The analysis must be performed at maximum 4 to 6 hours after collection. Provide rapid delivery of sample to the laboratory.

Dosing is by chromosomal method, with elongation of the clotting time, or chromogenic using LMWH yardstick.


Four hours after injection of LMWH, anti-Xa assay is included:

– Between 0.3 and 0.45 IU / mL for preventive use of LMWH;

– Between 0.5 and 1 IU / mL to venous thrombosis.



Practical advice:

This examination is unnecessary in monitoring treatment to LMWH, except in cases of obesity, which is poorly absorbed heparin. That’s why the nurse will ensure giving injections in   areas devoid of fat. This examination is also useful in renal impairment or in patients receiving treatment with high doses of heparin.


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