fibrinogenul

Fibrinogen is a soluble glycoprotein in vertebrate blood plasma and the principal precursor of fibrin in the coagulation cascade. It is synthesized by hepatocytes, circulates at about 2–4 g/L, and functions as the major substrate for thrombin during coagulation. In humans it is also known as coagulation factor I.

Molecularly, fibrinogen is a hexamer composed of two sets of three polypeptide chains (Aα, Bβ, and γ) linked by disulfide bonds. The molecule features central E and two distal D regions, which participate in the conversion to fibrin and the formation of a hemostatic meshwork. Thrombin cleaves fibrinopeptides from the Aα and Bβ chains, producing fibrin monomers that polymerize to form a clot. Factor XIIIa crosslinks the fibrin network to stabilize the clot.

Fibrinogen also acts as an acute-phase protein; its plasma levels rise in response to inflammation, infection, trauma, and pregnancy, while estrogen-containing therapies can increase levels. Conversely, congenital or acquired defects can lead to bleeding or thrombotic tendencies. Hypofibrinogenemia and afibrinogenemia (low or absent fibrinogen) cause bleeding, whereas dysfibrinogenemia involves qualitatively abnormal fibrinogen. Very high levels (hyperfibrinogenemia) are associated with inflammatory states and cardiovascular risk.

Clinical measurement of fibrinogen includes functional assays (Clauss method) that assess clot formation in the presence of excess thrombin, and antigenic assays that quantify total fibrinogen protein. Management of congenital deficiency may involve fibrinogen concentrates or cryoprecipitate, particularly around surgery or bleeding episodes.