Anti-Xa Assay Unit Converter

The anti-Xa assay is a blood test that measures how effectively an anticoagulant medication is inhibiting Factor Xa, a key enzyme in the blood clotting cascade. Factor Xa sits at the convergence point of the clotting pathway, where it helps convert prothrombin into thrombin, ultimately forming blood clots.

The test is primarily used to monitor heparin-based therapies (unfractionated heparin and low molecular weight heparins such as enoxaparin), fondaparinux, and direct oral anticoagulants (rivaroxaban, apixaban, edoxaban). Results are reported in IU/mL for heparin-based drugs or ng/mL for direct oral anticoagulants.

Unlike many biomarkers that reflect the body's own chemistry, the anti-Xa assay is a drug-monitoring test. It tells your doctor whether your anticoagulant dose is keeping you in the therapeutic window, balancing clot prevention against bleeding risk.

Factor Xa is the activated form of Factor X, which is produced in the liver. Factor X is a vitamin K-dependent protein that requires gamma-carboxylation to function in the clotting cascade, and it can be activated by both the intrinsic and extrinsic coagulation pathways.