Edoxaban is a reversible orally active factor Xa inhibitor approved in Japan for Venous ThromboEmbolism (VTE) prophylaxis in major orthopedic surgery and submitted for approval in multiple markets for Stroke Prevention in non-valvular Atrial Fibrillation (SPAF) and VTE treatment and recurrence prevention. Although routine monitoring is not required, determination of anti-Xa activity with results expressed in edoxaban plasma concentration may be helpful in some special clinical settings such as urgent invasive procedures or in cases of bleeding.We have developed a specific, automated, user-friendly assay for measuring plasma edoxaban-related anti-Xa activity using the STA® Liquid Anti-Xa with an edoxaban dedicated test set-up, along with specific edoxaban calibrator and control sets, namely STA® Edoxaban Calibrator and STA® Edoxaban Control, on the STA® line analyzers. These calibrator and control sets are freeze-dried in vitro edoxaban spiked citrated plasmas. Test results are expressed in ng/mL of edoxaban.Assay performances including Limit of Blank (LOB), Lower Limit of Detection (LLOD) both according to CLSI EP-17-A guideline, Lower Limit of Quantification (LLOQ), Upper Limit of Quantification (ULOQ) according to CLSI EP6-A guideline, with and without automated re-dilution of plasma sample, and within and between-run reproducibility have been determined.Anti-Xa assay results were compared to those obtained with Mass Spectrometry Liquid Chromatography (LC-MS) reference method to evaluate assay recovery.All study assays were performed using freeze-dried of frozen in vitro edoxaban-spiked citrated plasma samples.Main potential interferences, i.e., hemoglobin, non-conjugated bilirubin, and lipemia, have been assessed.Assay performance results are summarized in Table I.Table I:Main Edoxaban assay performances as determined during test developmentParameterResults obtained with prototype reagent batch and test set-upLOB10 ng/mLLLOD15 ng/mLLLOQ (preliminary estimation)20 ng/mLULOQWithout sample re-dilution150 ng/mLWith sample re-dilution450 ng/mLReproducibilityWithin run (n = 21)Freeze-dried controls40 ng/mL≤ 4.5%120 ng/mL≤ 6.0%Frozen spiked samples50 ng/mL≤ 7.1%100 ng/mL≤ 4.9%200 ng/mL≤ 4.3%350 ng/mL≤ 4.0%Between run (n = 10)Freeze-dried controls40 ng/mL≤ 7.0%120 ng/mL≤ 3.6%Frozen spiked samples50 ng/mL≤ 5.0%100 ng/mL≤ 4.0%350 ng/mL≤ 4.6%Recovery(freeze-dried samples)40 ng/mL87.4%120 ng/mL101.9%Edoxaban calibrator and control stabilityCalibratorsOnboard4 hoursControlsOnboard24 hours+2 – 8°C7 daysInterferencesHemoglobinNone up to 1 g/LNon-conjugated bilirubinNone up to 200 µMLipemiaNone up to 2.5 g/L (as Intralipid® concentration)In conclusion, the proposed edoxaban assay developed using STA® Liquid Anti-Xa reagent with a dedicated test set-up and specific STA® Edoxaban Calibrator and STA® Edoxaban Control sets allows an accurate, reproducible, automated, and user-friendly, edoxaban plasma concentration determination. Further studies are required to confirm assay performance in ex vivo samples. DisclosuresHerve:Diagnostica Stago: Employment. Beaufils:Diagnostica Stago: Employment. Kochan:Daiichi Sankyo: Employment. He:Daiichi Sankyo: Employment. Depasse:Diagnostica Stago: Employment.