Fibrinogen is a plasma protein precursor of fibrin, which polymerizes and becomes the main component of the fibrin clot. Fibrinogen is a protein of the inflammatory phase; its concentration increases during inflammation, infection, pregnancy and after trauma. A high level of fibrinogen is a significant risk factor for developing coronary artery and cerebrovascular diseases. A low fibrinogen level is found in congenital afibrinogenaemia. This level may also drop significantly when it is lost to the intravascular space (hemorrhage, shock).