PB1108 - Correlation of two low molecular weight heparin anti-Xa assays with apixaban and rivaroxaban calibrated assays

Background: Although monitoring of Factor Xa inhibitors such as apixaban and rivaroxaban is not required, detection of drug effect is useful in certain clinical scenarios, such as in determining need for anticoagulant reversal in bleeding patients or urgent surgery. Andexanet Alfa (Portola Pharmaceuticals Inc., South San Francisco, CA) and prothrombin complex concentrate (PCC) are two reversal/hemostatic agents for Xa inhibitors, but they carry thrombotic risk and are expensive. Anti-Xa assays with apixaban and rivaroxaban calibrators exist but are not routinely available, thus, there is a clinical need for a routine test to detect Factor Xa inhibitor effect.

Aims: To correlate Siemens INNOVANCE® Heparin and IL HemosIL Heparin anti-Xa assays with apixaban and rivaroxaban calibrated assays.

Methods: We prospectively consented patients admitted to Clements University Hospital in Dallas, TX between Feb 2021 – Feb 2022 who were taking rivaroxaban (n=58) or apixaban (n=100). Two different low molecular weight heparin (LMWH) anti-Xa assays were performed on each sample (Innovance Heparin, Siemens, Marburg, Germany; HemosIL Heparin, Instrumentation Laboratory Company, Lexington, MA). If results were > 1.5 IU/mL, the upper limit of detection for both assays, samples were diluted 1:1 or 1:5 with plasma and run to obtain discrete values. Previously validated apixaban and rivaroxaban-specific anti-Xa assays (Hyphen, Neuville-Sur-Oise, France) were concurrently run on their respective samples. Linear regression analysis was used to correlation between the two LMWH anti-Xa activities and the specific assays.

Results: Both LMWH anti-Xa assays showed excellent linear correlation (r=>95%) with the apixaban and rivaroxaban assays along a wide range of drug levels (see Figure 1 and Table 1).

Conclusion(s): LMWH anti-Xa assays can be used as a surrogate to detect clinically relevant amounts of apixaban and rivaroxaban for clinical decision making to use reversal/hemostatic agent in the setting of bleeding or urgent surgery.