PB0435 - Interference in point-of-care International Normalized Ratio monitoring in patients with lupus anticoagulant is correlated with anti-β2-Glycoprotein I antibody titers

Sunday, June 25, 2023

18:30 – 19:30 ET

Room: Exhibition

Presenting Author(s)

Tessa Noordermeer, MSc

PhD-candidate
Center for Benign Haematology, Thrombosis and Haemostasis, Van Creveldkliniek, University Medical Center Utrecht, Utrecht University, Utrecht, the Netherlands
Utrecht, Utrecht, Netherlands

Co-Author(s)

Rolf T. Urbanus, PhD

Associate professor
Center for Benign Haematology, Thrombosis and Haemostasis, Van Creveldkliniek, University Medical Center Utrecht, Utrecht University, Utrecht, the Netherlands
Utrecht, Utrecht, Netherlands
CW

Chong Y. Wong

Master student
Department of Rheumatology and Clinical Immunology, University Medical Center Utrecht, Utrecht University, Utrecht, the Netherlands
Utrecht, Utrecht, Netherlands
JJ

Janna J. Jansma

Master student
Central Diagnostic Laboratory, University Medical Center Utrecht, Utrecht University, Utrecht, the Netherlands
Utrecht, Utrecht, Netherlands
NW

Nynke M. Wiersma

MD
Department of Thrombosis and Anticoagulation, Diagnostic Center Saltro, Utrecht, The Netherlands
Utrecht, Utrecht, Netherlands
Minka Zivkovic, MSc

Ph.D. candidate
Center for Benign Haematology, Thrombosis and Haemostasis, Van Creveldkliniek, University Medical Center Utrecht, Utrecht University, Utrecht, the Netherlands
Utrecht, Utrecht, Netherlands
AH

Albert Huisman

Clinical Chemist
Central Diagnostic Laboratory, University Medical Center Utrecht, Utrecht University, Utrecht, the Netherlands
Utrecht, Utrecht, Netherlands
ML

Maarten Limper

MD
Department of Rheumatology and Clinical Immunology, University Medical Center Utrecht, Utrecht University, Utrecht, the Netherlands
Utrecht, Utrecht, Netherlands

Background: Patients with antiphospholipid syndrome (APS) receive anticoagulant therapy with vitamin K antagonists (VKA) to prevent recurrent thrombosis. VKA treatment requires strict monitoring with international normalized ratio (INR). It is known that lupus anticoagulant can lead to elevated INR results with point-of-care-testing (POCT) devices which could result in inadequate adaptation of anticoagulant therapy.

Aims: To determine discrepancies between POCT-INR and laboratory-INR in LA-positive thrombotic APS patients on VKA.

Methods: Paired INR testing was performed with one POCT device (CoaguChek XS) and two laboratory assays (Owren and Quick method) in 33 LA-positive thrombotic APS patients on VKA in a single-center cross-sectional study. Patients were tested for anti-β2-Glycoprotein I (β2GPI), anti-cardiolipin, and anti-phosphatidylserine/prothrombin (PS/PT) IgG and IgM antibodies. Agreement between assays was evaluated. Agreement limits were considered satisfactory if differences were ≤20% as determined by the Clinical and Laboratory Standards Institute (CLSI).

Results: We found poor agreement between POCT-INR and laboratory-INR based on a Lin’s concordance correlation coefficient (ρc) of 0.42 (95%-CI: 0.26-0.55) between POCT-INR and Owren-INR and a ρc of 0.64 (95%-CI: 0.47-0.76) between POCT-INR and Quick-INR (figure 1). Differences between INR methods became larger when POCT-INR values were >3.0. High nLA-ratios based on the dRVVT were more frequently observed in patients with an INR disagreement between POCT-INR and laboratory-INR. Antiphospholipid antibody titers were elevated in patients with an INR disagreement between POCT-INR and laboratory-INR of which high anti-β2GPI IgG antibody titers correlated best with the INR disagreement (Spearman’s ρ of 0.54, p=0.001 for POCT-INR and Owren-INR, ρ of 0.53, p=0.002 for POCT-INR and Quick-INR).

Conclusion(s): There is disagreement of INR values measured with POCT-INR and laboratory-INR in a proportion of patients with LA. Consequently, laboratory-INR monitoring should be preferred over POCT-INR monitoring in LA-positive APS patients, especially in patients with high anti-β2GPI IgG antibody titers or when the POCT-INR>3.0.