fibrinogeene

Fibrinogen, also known as coagulation factor I, is a soluble plasma glycoprotein produced primarily by the liver. It serves as the precursor to fibrin, the protein that forms the structural basis of a blood clot. In addition to its role in coagulation, fibrinogen acts as an acute-phase reactant, with levels rising in response to inflammation, infection, and pregnancy.

Fibrinogen is a hexamer composed of two identical sets of three polypeptide chains: Aα, Bβ, and γ. Thrombin cleaves fibrinopeptides from the Aα and Bβ chains, converting fibrinogen into fibrin monomers that polymerize to form a fibrin network. Factor XIIIa crosslinks the fibrin strands to stabilize the clot. Fibrinogen also supports platelet aggregation by binding to the platelet GPIIb/IIIa receptor, aiding in the formation and stability of the thrombus.

Synthesis and regulation occur mainly in the liver. Fibrinogen levels increase in response to inflammatory cytokines, especially interleukin-6. Normal plasma concentrations are roughly 2 to 4 g/L, though values vary with age, sex, and physiological conditions. Clinically, fibrinogen is measured by Clauss or nephelometric methods. Levels may decrease in liver disease, disseminated intravascular coagulation, or after massive transfusion, and may increase during acute inflammation, pregnancy, or estrogen therapy.

Clinical significance includes both quantitative and qualitative disorders. Congenital deficiencies, such as afibrinogenemia or hypofibrinogenemia, lead to bleeding tendencies. Dysfibrinogenemia describes structurally abnormal fibrinogen with impaired function. Conversely, elevated fibrinogen levels are associated with increased risk of thrombosis and cardiovascular disease and are used as an inflammatory marker in various conditions.