Abstract Number: PB0565
Meeting: ISTH 2020 Congress
Background: Patients on apixaban or rivaroxaban may not benefit from anticoagulant reversal strategies when their drug levels are below 30-50 ng/mL (ISTH, 2016). It is unknown if anti-Xa low molecular weight heparin (LMWH) assays can reliably detect drug levels in this range.
Aims: To establish if LMWH anti-Xa assays can identify patients with apixaban or rivaroxaban levels < 50 ng/mL.
Methods: We selected 100 clinical samples from Hamilton Regional Laboratory Medicine Program’s Special Coagulation Laboratory with known apixaban or rivaroxaban drug levels up to 100 ng/mL (determined using Diagnostica Stago’s STAr/Evolution analyzer with rivaroxaban and apixaban drug-specific calibrators). Three LMWH calibrated anti-Xa assays were performed for each sample using: Instrument Laboratories ACL TOP 300 (IL), Siemens BCS XP (Siemens) and Diagnostica Stago STAr/Evolution (Stago) as per manufacturer protocols, reagents and calibrators. We used linear regression and Pearson correlation coefficients to compare LMWH anti-Xa activities with drug levels. We determined the LMWH anti-Xa activity that corresponded to 95% negative predictive value (NPV) for an apixaban or rivaroxaban drug level greater than 50 ng/mL. The Hamilton Integrated Research Ethics Board reviewed this study.
Results: In 73 apixaban and 27 rivaroxaban samples, all 3 LMWH anti-Xa assays correlated linearly with drug levels (r=0.91 for apixaban, r=0.86-0.96 for rivaroxaban) (Figure 1). A LMWH anti-Xa activity below 0.26 U/mL (IL), 0.31 U/mL (Siemens), or 0.84 U/mL (Stago) had 95% NPV for an apixaban drug level > 50 ng/mL. A LMWH anti-Xa activity below 0.35 U/mL (IL), 0.50 U/mL (Siemens), or 1.34 U/mL (Stago) had 95% NPV for a rivaroxaban drug level > 50 ng/mL.
Conclusions: LMWH anti-Xa assays can identify patients who are unlikely to benefit from anticoagulant reversal. The predictive threshold varies widely between instrument/reagent combinations.
[Figure 1. LMWH anti-Xa activities corresponding to known drug levels of apixaban and rivaroxaban (n=100)]
To cite this abstract in AMA style:Mithoowani S, Gupta A, Moffat K, Carlino S, Crowther MA. Low Molecular Weight Heparin Calibrated Anti-Xa Assays can Identify Patients with Low Apixaban or Rivaroxaban Drug Levels [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/low-molecular-weight-heparin-calibrated-anti-xa-assays-can-identify-patients-with-low-apixaban-or-rivaroxaban-drug-levels/. Accessed November 30, 2023.
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