84 - Oral Communication
Diagnostic laboratory: Today & tomorrow
Feb. 26, 2021, 1:45 p.m. - 3:15 p.m., Sydney


A universal anti-Xa assay for the determination of rivaroxaban, apixaban, and edoxaban drug levels: development, diagnostic accuracy, and external validation
G. Willekens1, 2, J. D. Studt3, A. Mendez4, L. Alberio5, P. Fontana6, W. A. Wuillemin7, A. Schmidt8, L. Graf9, B. Gerber10, C. Bovet2, M. Nagler2, Presenter: G. Willekens1, 2 (1Maastricht, 2Bern, 3Zürich, 4Aarau, 5Lausanne, 6Geneva, 7Lucerne, 8Zurich, 9St. Gallen, 10Bellinzona)

Background and Objective
A universal anti-Xa assay for the determination of rivaroxaban, apixaban, and edoxaban drug levels would simplify laboratory procedures and facilitate widespread implementation. We aimed to develop and validate a universal anti-Xa assay to be used in clinical practice.
Following two pilot studies analyzing spiked samples and material from 625 patients, we conducted a prospective multicentre cross-sectional study, including 867 patients treated with rivaroxaban, apixaban, or edoxaban in clinical practice. Anti-Xa activity was measured by a universal assay calibrated to low-molecular weight heparin (LMWH) in addition to ultra‐performance liquid chromatography–tandem mass spectrometry (LC-MS/MS). As an external validation, anti-Xa activity was also determined in nine external laboratories.
Measurements of the universal anti-Xa assay correlated strongly with rivaroxaban, apixaban, or edoxaban drug levels (rs=0.94, 95% confidence interval, CI, 0.93 to 0.99; area under the receiver operating characteristics curve, AUC, 0.99). The sensitivity with regard to the clinically relevant cut-off levels 30 µg/L and 50 µg/L was 96.2% (95% CI 94.4, 97.4) and 96.4% (94.4, 97.7), respectively (specificity 92.9% and 93.3%). Concordant results were obtained in the external validation study (rs=0.96; AUC 0.98; sensitivity 95.78% and 97.44%; specificity 85.94% and 97.44%).
The universal anti-Xa assay based on an LWMH-calibration demonstrated a high accuracy in all phases of the evaluation project. Widespread implementation might simplify laboratory procedures and provide fast and reliable drug measurements in various healthcare settings.
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