fibriinogeeniin

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 fibrous protein that forms the mesh of a blood clot. Fibrinogen circulates at a relatively high concentration in blood and is essential for normal hemostasis.

Molecularly, fibrinogen is a hexamer composed of two sets of three polypeptide chains: Aα, Bβ, and γ. It is synthesized mainly in the liver and released into the plasma, with its production influenced by inflammatory signals such as interleukin-6. In adults, typical plasma levels range from about 2 to 4 g/L, and the protein has a half-life of roughly three to five days.

In the coagulation cascade, thrombin cleaves fibrinogen to form fibrin monomers by removing fibrinopeptides A and B. These monomers polymerize to form a fibrin network that stabilizes the clot, a process further strengthened by factor XIII crosslinking. Fibrinogen also supports platelet aggregation by binding to the platelet integrin GPIIb/IIIa, helping to form a stable platelet plug.

Clinically, fibrinogen levels are informative. Low levels (hypofibrinogenemia or afibrinogenemia) can cause bleeding, while elevated levels (hyperfibrinogenemia) are associated with inflammation, pregnancy, smoking, and increased cardiovascular risk. Fibrinogen is an acute-phase reactant, rising in response to inflammation. Laboratory assessment can measure antigenic fibrinogen concentration and functional fibrinogen (often by the Clauss method), with additional tests such as thrombin time used to interpret abnormalities.