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    Poster Networking

    Hemophilia and Rare Bleeding Disorders

    Poster Networking Session

    PB1228 - Inhibitor detection in acquired hemophilia A: a comparison between the Nijmegen modified Bethesda assay and an anti-FVIII ELISA

    Tuesday, June 27, 2023
    18:30 – 19:30 ET
    Room: Exhibition

      Presenting Author(s)

    • Mv

      Marie-Astrid van Dievoet, MD

      Clinical biologist
      Department of laboratory medicine, Cliniques universitaires St. Luc, Brussels Belgium
      Brussels, Brussels Hoofdstedelijk Gewest, Belgium

      • Co-Author(s)

    • Cedric Hermans, MD, PhD (he/him/his)

      Head Haemostasis and Thrombosis Unit
      St-Luc University Hospital
      Brussels, Brussels Hoofdstedelijk Gewest, Belgium

    • CL

      Catherine Lambert

      Hematologist
      Cliniques Universitaires Saint-Luc
      Brussels, Brussels Hoofdstedelijk Gewest, Belgium

    Background: The Nijmegen modified Bethesda assay (NBA) remains the gold standard for factor VIII (FVIII) inhibitor detection. However, patients with acquired hemophilia A (AHA) typically exhibit inhibitors with type 2 kinetics, which are difficult to interpret with a NBA. Detection of FVIII-binding autoantibodies by ELISA is said to be equally sensitive and specific for the diagnosis of AHA.

    Aims: We compared NBA and ELISA for the detection of FVIII inhibitors in AHA patients followed in our university hospital.

    Methods: Inhibitor concentration of ≥0.6 was defined as positive for NBA. Residual activity was measured with a one-stage FVIII assay using SynthasIL and HemosIL calibration plasma (Werfen, Barcelona). For patients on emicizumab residual FVIII activity was measured with a chromogenic assay using bovine reagents (Coamatic, Chromogenix, Werfen). ELISA was performed with Lifecodes factor VIII antibody screen (Immucor, Paris, France).

    Results: A total of 44 samples from 10 patients with AHA were analyzed with both NBA and ELISA. Results were concordant for 31 samples with both techniques: 26 were positive and 5 negative. For 10 samples we had a discrepancy with positive NBA (0.6-18.3 BU) and negative ELISA. These samples were issued from 5 different patients. One patient was never positive with ELISA during the course of his disease (lupus anticoagulant was ruled out). For the other 4 patients discrepant results were only seen during follow-up and not at diagnosis. In three samples (from 2 patients) a borderline NBA (0.4-0.5 BU) with a weak positive ELISA was seen.

    Conclusion(s): In our small patient group with AHA we saw several discrepant results between NBA and anti-FVIII ELISA. NBA was often positive with a negative ELISA. In the majority of patients this was seen in follow-up samples. These results should be taken into consideration when deciding which assay to perform for the detection of FVIII inhibitors.