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A specialist may request a quantitative factor Xa assay in a situation of overdose. [2] Andexanet alfa, a specific antidote to reverse the anticoagulant activity of direct Xa inhibitors in the event of major bleeding, was approved by the FDA in 2018. [9] It is also available in the UK. [10]
The methodology of an anti-factor Xa assay is that patient plasma is added to a known amount of excess recombinant factor X and excess antithrombin. If heparin or LMWH is present in the patient's plasma, it will bind to antithrombin and form a complex with factor X, inhibiting it from becoming factor Xa. [17]
Factor Xa also plays a role in other biological processes that are not directly related to coagulation, like wound healing, tissue remodelling, inflammation, angiogenesis and atherosclerosis. Inhibition of the synthesis or activity of Factor X is the mechanism of action for many anticoagulants in use today.
Surface plasmon resonance is an example of technique that can detect binding between an unlabeled antibody and antigens. [16] Another demonstrated labeless immunoassay involves measuring the change in resistance on an electrode as antigens bind to it.
The setting of reasonable cutoff limits help reduce false positive results that occur from assay limitations. Because of the social and legal consequences, a positive test result must be confirmed by an alternative method, usually Gas Chromatography/Mass spectrometry.
Functioning in a way similar to that of an ELISA or Western Blot, a two-antibody binding process is used to determine concentrations of analytes. MIA uses antibodies that are coating a magnetic bead. These anti-bodies directly bind to the desired pathogen or molecule and the magnetic signal given off the bound beads is read using a magnetometer.
A radioimmunoassay (RIA) is an immunoassay that uses radiolabeled molecules in a stepwise formation of immune complexes.A RIA is a very sensitive in vitro assay technique used to measure concentrations of substances, usually measuring antigen concentrations (for example, hormone levels in blood) by use of antibodies.
Thrombin time can be prolonged by heparin, fibrin degradation products, and fibrinogen deficiency or abnormality. Thrombin time is not affected by anti-Xa anticoagulants such as rivaroxaban or apixaban, but is very sensitive to direct thrombin inhibitors including dabigatran, argatroban, and bivalirudin. [5]