The normal function of Factor Xa (FXa) is to cleave its natural substrate, prothrombin, to generate thrombin, the enzyme responsible for the formation of the fibrin clot.
In the presence of heparin, competition occurs between this mechanism and the inhibitory mechanism exerted by the heparin-antithrombin complex, this inhibition being largely responsible for the anticoagulant action of heparin.
The principle for Apixaban, Edoxaban and Rivaroxaban is slightly different as they do not work via antithrombin but work directly against FXa.
Anti-Xa is an analytical test performed in the laboratory that is used to quantify the amount of Apixaban, Edoxaban, Rivaroxaban and Low Molecular Weight Heparin in the patients sample, therefore it is imperative that when requesting this test the specific drug the patient is taking is stipulated on the request form.
For clinical relevance and reference range of an individual drug click the link above.
The volume of blood in coagulation samples must lie within the volume range as indicated by the size of the black fill arrow present on tubes. Volumes above or below the arrow will result in sample rejection to ensure validity of results.
Age of Sample
Samples will be rejected if received more than 1 hours post venepuncture.
- 2 blue top (sodium citrate) samples
- all coagulation tubes must be adequately filled (see above)
- All coagulation tubes must be mixed several times by gentle inversion immediately after venepuncture. Mixing the sample with the anticoagulant stops the sample clotting within the tube.
- It is not possible to provide results on clotted, insufficient, lipaeamic or haemolysed samples. These samples will be rejected with the appropriate comment.
- Samples tubes that have expired cannot be accepted