Fatal Hemorrhage in a Patient with an Acquired Inhibitor of Human Thrombin

Thrombin (factor IIa) is a serine protease that performs a number of functions in blood coagulation.1 Among its most important actions is converting fibrinogen into fibrin monomers, which polymerize to form the fibrin clot. Thrombin participates in the activation of factors V, VIII, and XIII, as well as of platelets.2 By binding to thrombomodulin on vascular endothelial cells, it forms a complex that activates protein C, thereby limiting the extent of an emerging clot.3 Cleavage of thrombin's inactive zymogen precursor, prothrombin (factor II), is required to generate functionally active thrombin. Acquired inhibitors of certain coagulation factors are relatively common, but . . .