PB0985 - Evaluating a "universal" calibrator for anti-Xa testing in patients taking rivaroxaban and apixaban

Tuesday, June 25, 2024

13:45 – 14:45 ICT

Room: Exhibition Hall

Presenting Author(s)

Emma J. Leitinger, MBBS BMedSci FRACP FRCPA

Haematologist, PhD Candidate
Monash Health
Melbourne, Victoria, Australia

Co-Author(s)

JC

Joanne Clifford

Senior Coagulation Scientist
Monash Pathology, Monash Health
Melbourne, Victoria, Australia
DR

Danielle Robinson

Haematology Registrar
Alfred Health
Melbourne, Victoria, Australia
CS

Clare Shugg

Senior Coagulation Scientist
Melbourne Health Pathology
Melbourne, Victoria, Australia
SL

Shujun Liu

Senior Coagulation Scientist
Alfred Pathology, Alfred Health
Melbourne, Victoria, Australia
AS

Alison Slocombe

Haematologist
Melbourne Health
Melbourne, Victoria, Australia
AW

Andrew Wallis

Principal Scientist
Monash Pathology, Monash Health
Melbourne, Victoria, Australia
GK

Giles Kelsey

Haematologist, Head of Haematology Laboratory
Melbourne Health Pathology
Melbourne, Victoria, Australia
SM

Susan Morgan

Haematologist, Head of Haematology Laboratory
Alfred Pathology, Alfred Health
Melbourne, Victoria, Australia
ZK

Zane Kaplan

Haematologist
Monash Health, Alfred Health
Melbourne, Victoria, Australia
SC

Sanjeev Chunilal

Director, Laboratory Haematology
Monash Health
Clayton, Victoria, Australia

Background: In critical bleeding, anti-Xa levels can assist decision-making around reversal agents for patients receiving apixaban and rivaroxaban. Whilst most laboratories routinely perform standard anti-Xa assays using a Low molecular weight heparin (LMWH) calibrator, drug-specific anti-Xa assays are often not readily available in an urgent setting. Consensus guidelines define rivaroxaban or apixaban (DOAC) levels below 50ng/mL and 30ng/ml as safe for standard and high-risk procedures respectively. Therefore, determining DOAC levels corresponding to 50ng/ml and 30ng/ml using a LMWH calibrator could address this unmet need.

Aims: To describe the correlation between rivaroxaban and apixaban levels using drug-specific and LMWH calibrators at 3 sites using different reagent/analyser combinations.
To define potential LMWH anti-Xa cut-points corresponding to drug levels of 30ng/mL and 50ng/mL.

Methods: One-hundred frozen plasma samples from patients on rivaroxaban and apixaban (50 samples per drug) were run at each laboratory using site specific analyser/reagents. Each sample batch comprised 20 with anti-Xa levels 20-50ng/mL and 50-100ng/mL, and 10 samples 100-200ng/mL. Samples were analysed with drug-specific and LMWH calibrators. Regression modelling was performed, and R2 and p values were calculated. Cut-points corresponding to drug levels of 30ng/mL and 50ng/mL were determined.

Results: Strong correlations were observed between drug-specific and LMWH anti-Xa activity with all reagent-analyser combinations (Figure 1). Linear regression demonstrated significant correlation at site 1, R2 0.99, p< 0.001. Quadratic models best defined correlations at sites 2 (R2 0.93, P< 0.001) and 3 (R2 0.94, P< 0.001). Combined DOAC cut-points corresponding to DOAC levels of 30ng/mL and 50ng/mL were: 0.17U/mL and 0.34U/mL for site 1, 0.52U/mL and 0.99U/mL for site 2, and 0.54U/mL and 0.89U/mL for site 3. Additional model calculations are shown in table 1.

Conclusion(s): The strong correlation between LMWH and drug-specific calibrators at all sites suggests that standard anti-Xa assays could be used to exclude clinically relevant DOAC levels in time critical scenarios.