Use of heparin calibrated anti-Xa assay for apixaban and rivaroxaban measurement in the context of regional telestroke activity

Abstract

In Bordeaux University Hospital, neurologists are required to prescribe thrombolysis using telemedicine (telethrombolysis) for anticoagulated stroke patients admitted in peripheral centers in the Nouvelle-Aquitaine region. However, due to the bleeding risk, the maximum concentration of DOAC authorizing thrombolysis is 30, 50 or 100 ng/mL (depending on the sources and the patient-specific benefit-risk ratio). Most of the time, specific assays of Direct Oral Anticoagulants (DOACs) are not available in these peripheral centers. We therefore studied an alternative test: the Unfractionated Heparin (UFH) anti-Xa activity which is available in most laboratories and could be used to estimate the DOAC concentration. Five centers were included in our study: three centers using the Liquid Anti-Xa HemosIL® Werfen reagent and two centers using the STA-Liquid Anti-Xa® Stago reagent. For each reagent, we established correlation curves between DOAC and UFH anti-Xa activities and determinated UFH cut-offs for the thresholds of 30, 50 and 100 ng/mL respectively. A total of 1455 plasmas were tested. There is an excellent correlation between DOAC and UFH anti-Xa activities using a third-degree modeling curve, independently the reagent used. However, a significant inter-reagent variability is observed concerning the obtained cut-offs. Our study makes unsuitable the use of a universal cut-off. In opposition to recommendations made by other publications, the UFH cut-offs must be adapted to the reagent used locally by the laboratory, and to the considered DOAC.