Factor VIII Inhibitor Assays: Methodology, Shortcomings,
and Challenges
M van Geffen1, M Dardikh1 and B Verbruggen
Affiliation: Laboratory of Hematology, Department of Laboratory Medicine, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands
A B S T R A C T
Development of inhibitory antibodies against factor VIII is a serious complication in the treatment of hemophilia patients, as theseantibodies inactivate factor VIII, resulting in an increased bleeding tendency and morbidity. The clinical manifestation of inhibitors has to be analyzed by objective laboratory tests to specify the exact nature of the inhibitor. Here, the inhibitor assays, especially the Bethesda assay and the Nijmegen assay, are discussed including their methodological shortcomings. This paper also discusses the epitope specificity of the inhibitor assays and the methods to investigate the specificity of inhibitors against factor VIII concentrates that may contribute to improve the treatment of hemophilia A patients with inhibitors. Finally, the use and limitations of overall clotting assays, such as clot wave form analysis, thromboelastography, and thrombin generation assay, in the management of hemophilia A patients with inhibitors are discussed.
Keywords: hemophilia A, factor VIII inhibitors, Nijmegen assay, Bethesda assay, epitope specificity
Correspondence: B Verbruggen, Laboratory of Hematology, Department of Laboratory Medicine, Radboud University Nijmegen Medical
Center, PO Box 9101, 6500 HB Nijmegen, The Netherlands. Tel: (31)-243614796; e-mail: H.Verbruggen@chl.umcn.nl
Factor_VIII_Inhibitor_Assays_Methodology__Shortcomings.pdf
Factor VIII Inhibitor Assays
1. INTRODUCTION
- FVIII 단백은 265kDa 크기의 단백질
- A1,A2,B,A3,C1,C2 Domain 으로 구성되어져 있고 vWF에 공유결합
Thrombin에의해 활성화 되면 B도메인이 떨어져 나가고 A1,A2,A3,C1,C2 으로 구성된 heterotrimer로 절단1
B 도메인은 FVIII 활성에 필수적이지 않으며 활성화 후 소실됨2
- 항체는 혈우병 치료에 주요한 문제3
외부에서 주입된 FVIII 단백질에 대한 IgG(alloantibody)외에 자가항체(후천성 혈우병)에의한 항체형성이 있을 수 있음
- 항체는 주로 A2(R484-I508)도메인, C2(E2181 to V22430)도메인 그리고 A3와 C1도메인에서 생성.4
A2 = FIXa 결합부위, C2=부분적으로 vWF및 인지질의 결합 영역을 나타낸다. 이들 부위에 항체가 결합되면
FVIII의 기능을 하지 못하게되여 이환율과 사망율이 증가 출혈경향이 높아진다. 5
- 항체검사는 스크리닝 검사시 혹은 비정상적인 출혈이나 응고인자 대체요법에 대한 반응이 좋지 않은 경우에 의심
항체의 조기발견은 초기에 치료를 가능하게 하고 출혈과 수술에 효과적인 지혈 치료를 할 수 있는 기회를 제공6
ITI 치료를 받고 있는 환자에게 치료효과를 모니터링 하기위해 측정되고
새로운 FVIII 제품의 면역원성을 시험하기 위해 측정됨
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