Abstract Number: PB1924
Meeting: ISTH 2020 Congress
Background: Patients with thrombotic complications of APS are at increased risk of recurrent thrombotic events and are recommended to have lifelong anticoagulation, usually with vitamin K antagonists (warfarin). Warfarin requires monitoring of the international normalised ratio (INR), since the anticoagulant effect is unpredictable. Monitoring INRs using POCT for patients with APS is often considered unreliable due to potential interactions of antiphospholipid antibodies with reagents used to calculate INR by POCT.
Aims: The aim of this study was to review reliability of POCT in APS patients whose anticoagulation is monitored at Guys and St. Thomas’ (GSTT) anticoagulation clinic.
Methods: We conducted a retrospective analysis of paired POCT and venous INR results (n=70) from 32 patients with APS (aged 28-78 years, 7 male & 25 female) monitored at GSTT (July 2018-January 2020) using a Coaguchek XS device. Six-month TTR of APS POCT, APS venous and non-APS POCT cohorts was also compared.
Results: Excluding paired samples with POCT INR >= 4.5, demonstrated a concordance of 92% of samples within an INR of 0.5 (n=50). 76% of paired samples had an acceptable INR variation of within 0.5 for the APS POCT cohort. POCT manufacturers do not advise interpreting INR results >= 4.8 since they cannot guarantee accuracy above this. Bland-Altman concordance analysis (Figure 1) showed high concordance between POCT and venous testing excluding INR >= 4.5. The mean six-month TTR for the APS POCT population was 48.37% (+-23.9, n=70), compared to 56.3% (+-21.4, n=174) in our venous testing cohort and 70% (+- 23.5, n=35) in non-APS patients using POCT.
Conclusions: Our results show good concordance between INR results obtained by POCT and venous sampling methods in APS patients and similar TTRs between APS POCT and non-POCT. INR POCT is a potential alternative to venous sampling for patients with APS when INR < 4.5 but requires further study.
[A Bland-Altman plot of the agreement between venous and POCT INR testing in APS excluding INR >= 4.5]
To cite this abstract in AMA style:Masucci M, Martin J, Shingleton E, Li Kam Wa A, Mahir Z, Breen K. Vitamin K Antagonist (VKA) Monitoring Using Point of Care Testing (POCT) in Patients with Antiphospholipid Syndrome (APS) [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/vitamin-k-antagonist-vka-monitoring-using-point-of-care-testing-poct-in-patients-with-antiphospholipid-syndrome-aps/. Accessed May 16, 2022.
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