fibrinogens

Fibrinogens are soluble plasma glycoproteins produced by the liver and circulating at about 2–4 g/L. They are essential components of the coagulation system, serving as the substrate that thrombin converts into fibrin to form a blood clot.

Each fibrinogen molecule is a dimer of three polypeptide chains (Aα, Bβ, and γ) arranged in two identical halves, with the polypeptides linked by disulfide bonds. It is a 340-kDa glycoprotein encoded by three genes (FGA, FGB, FGG) on chromosome 4.

During coagulation, thrombin cleaves fibrinopeptides A and B from the Aα and Bβ chains, converting fibrinogen to fibrin monomers that polymerize to form a network. Factor XIIIa then cross-links adjacent fibrin molecules, stabilizing the clot.

Fibrinogen is produced by hepatocytes and acts as an acute-phase protein, rising in response to inflammatory cytokines. Normal plasma levels vary with sex and age but broadly range from 2 to 4 g/L. Levels can increase in infection, inflammation, and pregnancy.

Clinical relevance includes elevated fibrinogen being a risk factor for thrombosis and cardiovascular disease, while low levels or dysfunctional fibrinogen cause bleeding disorders. Congenital disorders include afibrinogenemia, hypofibrinogenemia, and dysfibrinogenemia. Acquired disturbances occur in liver disease and disseminated intravascular coagulation.

Laboratory assessment employs the Clauss functional fibrinogen assay and antigenic measurements. Treatment for deficiency may involve cryoprecipitate or fibrinogen concentrate, depending on cause and severity.

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