Article Sections

Introduction

Hemophilia is a genetic disorder characterized by a deficiency in specific coagulation factors, leading to abnormal bleeding.  The term hemophilia typically refers to the 2 most common coagulation factors affected:  factor VIII (hemophilia A) and factor IX (hemophilia B).  Patients develop bleeding patterns consistent with a disorder in secondary hemostasis (eg, delayed postsurgical bleeding, deep tissue bleeding).

Pathophysiology and risk factors

Hemostasis is a physiologic mechanism aimed at maintaining the integrity of the closed circulatory system.  Following endothelial injury, a series of coordinated events occur to repair the loss of vascular integrity and prevent further bleeding:

  • Vasoconstriction:  Immediate narrowing of blood vessels occurs to reduce blood flow.
  • Primary hemostasis (platelet plug formation):  With the help of von Willebrand factor ( Figure 1) (vWF), platelets adhere to the exposed subendothelial matrix and aggregate to form a temporary hemostatic plug, laying the foundation for formation of the fibrin clot.

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