Abstract
BACKGROUND: Direct oral anticoagulants (DOACs) interfere with clot-based assays, including factor (F)VIII testing and the Nijmegen-Bethesda assay, potentially leading to false-positive results for FVIII inhibitors. Misinterpretation of these results carries serious clinical consequences. Activated charcoal-based products, such as DOAC Remove, may restore assay accuracy, but data supporting their use in FVIII inhibitor assays are limited. OBJECTIVES: In this study, we aim to determine DOAC interference in FVIII inhibitor testing and evaluate effectivity of DOAC removal to restore assay reliability. METHODS: Normal pooled plasma was spiked with therapeutic and supratherapeutic concentrations of apixaban, edoxaban, rivaroxaban, and dabigatran. Plasma pools from persons with acquired hemophilia A were spiked with DOACs and retested with and without DOAC removal treatment to evaluate workflow performance. FVIII inhibitor activity was measured with and without activated charcoal-based DOAC removal to establish DOAC interference and removal efficacy. RESULTS: Spiking experiments with DOACs caused concentration-dependent false-positive FVIII inhibitor results (>0.6 Nijmegen Bethesda Units/mL), with dabigatran showing the strongest interference and apixaban the weakest. DOAC removal substantially reduced or eliminated interference across all drugs. Post-removal FVIII inhibitor values closely matched baseline concentrations in both spiked normal pooled plasma and pooled patient plasma, with most results within ±20% of the assay variability. CONCLUSION: DOACs significantly interfere with FVIII inhibitor assays, potentially causing clinically significant false-positive results. Activated charcoal-based DOAC removal treatment provides a practical solution to restore assay reliability. These findings support the integration of DOAC removal into anti-FVIII testing protocols for patients on anticoagulant therapy.