PB0645 - Evaluation of the Effect of Factor VIII on the Measurement of Emicizumab Levels in Plasma

Monday, June 26, 2023

18:30 – 19:30 ET

Room: Exhibition

Presenting Author(s)

PG

Paula E. Grennan, BSc and MSc

Medical Scientist
St. James's Hospital, Dublin
Dublin, Dublin, Ireland

Co-Author(s)

MB

Mary Byrne

Coagulation Laboratory Chief
National Coagulation Centre, St James's Hospital, Dublin
Dublin, Dublin, Ireland
Mairead Doyle, MSc

Medical Scientist
National Coagulation Centre, St James's Hospital, Dublin
Dublin, Dublin, Ireland
Michelle Lavin, MB, PhD (she/her/hers)

Consultant Haematologist
National Coagulation Centre, St. James Hospital and Irish Centre for Vascular Biology, School of Pharmacy and Biomolecular Sciences, Royal College of Physicians and Surgeons in Ireland (RCSI)
Dublin, Dublin, Ireland
JO

James S. O'Donnell, MB, PhD

Professor of Haematology
Irish Centre for Vascular Biology, Royal College of Surgeons in Ireland,Dublin, Ireland
Dublin, Dublin, Ireland
NO

Niamh O'Connell, MD

Consultant Haematologist
National Coagulation Centre, St James's Hospital, Dublin
Dublin, Dublin, Ireland
KR

Kevin Ryan

Consultant Haematologist
National Coagulation Centre, St James's Hospital, Dublin
Dublin, Dublin, Ireland

Background: Emicizumab, a factor VIII (FVIII) mimetic, is used as prophylaxis treatment in persons with severe haemophilia A (PwSHA). A modified one stage FVIII assay for emicizumab (EMI-mOSA) can be utilised to measure plasma emicizumab levels. Endogenous or exogenous FVIII will interfere with the measured emicizumab level due to its similar mechanism of action.

Aims: To evaluate the extent of the FVIII effect in the EMI-mOSA assay.

Methods: Samples were collected (n=23), from a reference cohort (no bleeding disorder or emicizumab treatment). The EMI-mOSA and the one stage FVIII:C clotting assay (OSA) was performed.
A spiking study was also performed using a series of test mixtures (n=8), containing a standard emicizumab concentration (91 µg/mL), in equal volumes with plasma containing varying FVIII concentrations (0.02-2.21 IU/mL). The EMI-mOSA and a bovine chromogenic (BoCHR) FVIII:C assay (ElectrachromeTM Factor VIII. HemosIL®), insensitive to the presence of emicizumab; was performed.

Results: EMI-mOSA results for the reference cohort ranged from 8.5-23.5 µg/mL, correlating with increasing FVIII levels (OSA: 0.73-2.45 IU/mL) (R2=0.965, p= < 0.001).
Emicizumab levels in the spiking study mixtures were expected to be 45.5 µg/mL with FVIII levels ranging from 0.01-1.10 IU/mL, accounting for the 1:1 dilution in test mixture. EMI-mOSA results ranged from 45.9-75.3 µg/mL, correlating with increasing FVIII levels (BoCHR: 0.02-1.21 IU/mL) (R2=0.975, p= < 0.001).
The measured increase above expected emicizumab levels ranged from 121% (emicizumab 55.2 µg/mL, FVIII 0.27 IU/mL) to 165% (emicizumab 75.3 µg/mL, FVIII 1.21 IU/mL). A negligible effect was measured at a FVIII level of 0.13 IU/mL (emicizumab 47.2 µg/mL).

Conclusion(s): FVIII interferes with EMI-mOSA results, confirmed by a measured result in the reference cohort. The extent of interference even at low levels of FVIII was identified by the spiking study. EMI-mOSA results should be interpreted in conjunction with a BoCHR FVIII:C assay, which will detect the presence of FVIII in a sample.