PB1077 - Evaluation of Automated Mixing Studies and Calculation of Index of Circulating Anticoagulant in Samples with Lupus Anticoagulant or Factor VIII Inhibitors

Tuesday, July 12, 2022

6:30 PM – 7:30 PM

Location: Exhibition

Presentation Format: In-Person

Presenting Author(s)

Shapla Kamali

Specialist Biomedical Scientist
Haematology and Blood Transfusion Laboratory, Newham University Hospital, Barts Health NHS Trust
London, England, United Kingdom

Co-Author(s)

Sean Platton, MSc CSci FIBMS

Consultant Biomedical Scientist
Royal London Hospital Haemophilia Centre, Barts Health NHS Trust
London, England, United Kingdom

Background: Samples with prolonged clotting times often have mixing tests performed, but interpretation is often problematic. Software on Sysmex CN-series analysers automates testing for immediate-acting and delayed-acting inhibitors, calculating index of circulating anticoagulant for immediate- (ICA) and delayed- (ICA_D) inhibitors, and compares them by division (ICA_D/ICA) and subtraction (ICA_D-ICA).

Aims: To evaluate the software and identify which reagent is most suitable for detecting immediate- and delayed-acting inhibitors.

Methods: Haemophilia patients with no detectable inhibitor (HPA) were used as controls. Three sample sets were analysed: congenital or acquired haemophilia A with inhibitors (INH); lupus anticoagulants by DRVVT and LA-sensitive APTT (LA); on rivaroxaban (DOAC). Samples were tested neat and at 50:50 dilution with normal plasma immediately after mixing; the 50:50 mix was incubated for two hours and re-tested along with neat samples and normal plasma. Samples were tested with five different APTT reagents: Actin FS (AFS); Actin FSL (FSL); Pathromtin SL (PSL); Cephen; and Cephen LS (CLS).

Results: ICA and ICA_D in LA samples were the same as or lower than in HPA samples with all reagents except CLS. ICA_D was higher than ICA in INH samples and higher than in HPA samples with all reagents, so ICA_D/ICA and ICA_D-ICA both identify INH samples. DOAC samples had higher ICA and ICA_D than in HPA samples with all reagents.

Based on cut-offs derived from HPA controls, reagents had sensitivity/specificity for LA of 0.0%/79.2%, 11.1%/83.7%, 0.0%/76.9%, 0.0%/82.1% and 55.6%/78.4%; and for INH 76.5%/100.0%, 64.7%/100.0%, 86.7%/96.8%, 85.7%/100.0% and 71.4%/100.0% for AFS, AFSL, PSL, Cephen and CLS respectively.

Conclusion(s): The software is suitable for use to detect immediate- and delayed-acting inhibitors. Of the reagents tested, Cephen LS was the best reagent to detect LA; all reagents identified INH. Care needs to be taken to exclude DOAC as a cause of a prolonged APTT to avoid misinterpretation.