PB1080 - The validation of mixing test-specific cut-off in lupus anticoagulant mixing test interpretation for multiple reagents

Tuesday, July 12, 2022

6:30 PM – 7:30 PM

Location: Exhibition

Presentation Format: In-Person

Presenting Author(s)

Osamu Kumano, PhD

Project Coordination Manager
HYPHEN BioMed
Neuville Sur Oise, Centre, France

Co-Author(s)

Gary W. Moore, DBMS

Professor
Department of Haematology, Specialist Haemostasis Unit, Cambridge University Hospitals NHS Foundation Trust, Cambridge, United Kingdom
London, England, United Kingdom

Background: Lupus anticoagulants (LA) are detected by prolongation of clotting times for activated partial thromboplastin time (APTT), dilute APTT (dAPTT) and dilute Russell’s viper venom time (dRVVT) screening tests. Mixing tests to evidence inhibition are recommended for LA detection, and interpretation via mixing test-specific cut-off (MTC) is recommended due to the high sensitivity in ISTH latest guidelines [1].

Aims: To investigate the sensitivity and specificity of APTT, dAPTT and dRVVT reagents and the distributions of LA-positive and factor deficient groups in mixing test-specific cut-off for multiple reagents.

Methods: One hundred-five samples from non-anticoagulated LA-positive patients, 52 factor deficient samples, and 25 non-LA warfarin samples were employed. Samples were tested with 4 APTTs, 1 dAPTT and 2 dRVVT reagents, all elevated screen ratios were followed up with mixing tests and mix ratios were also calculated. The frequencies of elevated and non-elevated results were calculated.

Results: The frequencies of screen ratio elevated results were 33.3-62.9%, 84.6-98.1% and 88.0-100% for APTT/dAPTT and 61.9-69.5%, 32.7% and 100% for dRVVT in LA-positive, factor deficient and warfarin samples, respectively. The distributions of mix ratio in LA-positive were wider than those of factor deficient and warfarin samples in all reagents. The frequencies of mix ratio elevated results were 45.5-83.6%, 0-88.0% and 12.0-80.0% for APTT/dAPTT and 72.3-80.8%, 35.3-94.1% and 88.0-96.0% for dRVVT, respectively.

Conclusion(s): The distributions of LA-positivity were overlapped with those of factor deficient and warfarin samples in low values. The frequencies of screen ratio and mix ratio elevated results were dependent on the reagents. It is important to understand the characteristics of the reagents and the confirmatory tests should be performed in samples which are suspected in the mixing tests.
[1] KMJ. Devreese et al. J Thromb Haemost. 2020; 18: 2828-2839.