PB1071 - Routine Measurement of Direct Factor Xa Inhibiting Anticoagulants

Background: The licensing of andexanet alfa for the reversal of rivaroxaban in bleeding patients with levels above 50ng/mL means direct factor Xa inhibitor (DFXaI) assays may be urgently required.

Sysmex CS-series analyser standard protocols for Hyphen-Biomed Heparin LRT [HB-LRT] reagents use different control and sample dilutions for each DFXaI (rivaroxaban 1/10; edoxaban 1/15; apixaban 1/20), making the assays uneconomical to run in laboratories with small numbers of DFXaI requests. Centralised testing in our Trust led to delays in DFXaI results, frequently >24h.

Aims: A combined protocol for all DFXaI with a single set of controls for all assays was evaluated for its potential to make assays available at all sites, on demand.

Methods: HB-LRT Heparin reagents were used with the standard protocols and the combined protocol, which uses a 1/15 sample dilution.

Samples were measured on a Sysmex CS-2100 using standard protocols, and on Sysmex CS-5100 and CS-2500 analysers using the combined protocol.

Hyphen-Biomed Rivaroxaban Controls 1 and 2 were tested five times a day for five days using the standard protocols for apixaban and edoxaban, to derive target values for use in the combined assay.

Results: Using drug-specific calibrators in the combined protocol, the difference in optical density between highest and lowest calibrators was not significantly different from those in dedicated rivaroxaban or apixaban assays.

Standard and combined protocols showed good correlation for patients samples.

Standard and combined protocols showed comparable precision and accuracy for control samples. Target values for new batches of control are derived from parallel testing with the existing batch, with target SDs calculated from measurement uncertainty data.

Performance in external quality assurance is acceptable for all analysers at all sites.

Conclusion(s): Rivaroxaban, apixaban and edoxaban assays are now available routinely, with the same turnaround time as all other routine clotting assays at Trust sites where the assay is available.