Abstract Number: PB0566
Meeting: ISTH 2020 Congress
Background: Screening and titration of factor VIII inhibitors allows monitoring of hemophilia A (HA) treatment and the diagnosis of acquired hemophilia. The classic Bethesda assay is based on the FVIII one stage clotting assay (BOSA) which can be impacted by the presence of lupus anticoagulants or interfering treatments.
Aims: The aims of this study was to compare analytical performances of the modified Bethesda assay using FVIII chromogenic assay (BCH) and BOSA.
Methods: The intra and inter assay precisions of the 2 techniques were calculated on a weak positive (1UB) control (Cryopep®). For 180 samples (20 patients with suspected acquired HA, 79 HA patients with or without inhibitors, 11 HA patients treated with Hemlibra®), inhibitor titers were determined by BCH (COAMATIC, Chromogenix, bovine reagents) and BOSA (Synthasil, Hemosil, deficient FVIII, Werfen). Calculated residual FVIII levels and inhibitor titers were then statistically compared (Mann and Whitney test and calculation of the kappa cohen coefficient).
Results: The intra assay CV on the positive control was 3% and 10% respectively for BCH and BOSA. The inter assay CV determined on the positive control was 10.7% for BCH and 17.5% for BOSA. The coefficients of correlation of residual FVIII and titers obtained on the 180 samples were 0.75 and 0.94 respectively (Figure 1). The titers obtained for the 53 positive plasmas were not significantly different between the two assays (P=0.859) except titers of HA patients treated with emicizumab significantly higher (+15%) with BCH. The approval rate between both techniques were 98.3% (kappa :0.96) with only 3 discrepancies:
1. plasma with LA weakly positive (0.8 UB) with BOSA and negative with BCH
2. plasmas weakly positive (0.6 and 0.8 BU) only with BCH (suspected Acquired HA and severe HA with a history of inhibitors).
Conclusions: Bethesda technique using chromogenic assay improves performance and appears to improve specificity.
To cite this abstract in AMA style:Nougier C, Jousselme E, Sobas F, Lienhart A, Négrier C. Bethesda Assay for the Detection and Titration of an Anti-VIII Inhibitor: Interest of the Chromogenic Assay [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/bethesda-assay-for-the-detection-and-titration-of-an-anti-viii-inhibitor-interest-of-the-chromogenic-assay/. Accessed May 18, 2021.
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