The assay is based on the inhibition of FXa by antithrombin (AT) in the presence of heparins.
The residual FXa hydrolyzes the chromogenic substrate which releases paranitroaniline (pNa).

The measurement is made at 405 nm. The patient's plasma is not supplemented with exogenous AT.
The anti-FXa measurement is therefore related to the antithrombin in the patient's plasma.

• 1 vial x 4 mL chromogenic substrate, lyophilized
• 1 vial x 4 mL bovine FXa, lyophilized
• 1 vial x 20 mL Tris-EDTA buffer, pH 8.4