Blood clots are complex structures composed of blood cells and proteins held together by the structural framework provided by an insoluble fibrin network. Factor (F)XIII is a protransglutaminase essential for stabilizing the fibrin network. Activated FXIII(a) introduces novel covalent crosslinks within and between fibrin and other plasma and cellular proteins, and thereby promotes fibrin biochemical and mechanical integrity. These irreversible modifications are also major determinants of …