Haematology & Oncology

Haemophilia

Haemophilia is an inherited deficiency of factor VIII (haemophilia A) or factor IX (haemophilia B), causing impaired fibrin formation and a characteristic tendency to bleed into joints, muscles and deep tissues; urgent specialist treatment is needed for significant bleeding or procedures.

Definition

Haemophilia is an inherited coagulation disorder caused by deficiency or dysfunction of factor VIII in haemophilia A or factor IX in haemophilia B. It is usually X-linked and causes impaired fibrin formation. Severity is graded by residual factor activity and should be interpreted alongside the person's bleeding phenotype and treatment history.

First principles

A factor deficiency impairs the thrombin burst

Factors VIII and IX support the intrinsic tenase complex that amplifies factor X activation and thrombin generation. Deficiency does not prevent an initial platelet plug, but the plug is poorly reinforced by fibrin, so bleeding may be delayed, prolonged and deep rather than immediately mucocutaneous.

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