Fibrinogen

Author: Prof. Dr. med. Peter Altmeyer

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Last updated on: 29.10.2020

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Synonym(s)

Factor I

Definition
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Fibrinogen, a glycoprotein, is a substrate of thrombin that splits off fibrinomers from fibrinogen. It belongs to the group of acute-phase proteins and is synthesized in the liver. The molecular weight is 340 kD and consists of two sets of three covalently bound polypeptide chains.

The activation of platelets leads to a structural change of the integrin receptor, which can then bind fibrinogen with high affinity. The consequence is a cross-linking of the platelets by fibrinogen. This can be the initial ignition for the production of a thrombus.

Fibrinogen is present in the blood in dissolved form. When a tissue is injured, a cascade-like process of activation of the procoagulatory factors circulating in the plasma is triggered on the surface of the activated platelets. This results in the formation of the enzyme thrombin from its precursor, prothrombin. Thrombin(factor II) sequentially cleaves the fibrinopeptides A (fibrinopeptide-A) and B (fibrinopeptide-B) from the A-alpha and B-beta chain of the protein complex. The fibrin monomers thus released polymerize spontaneously to form water-insoluble fibrin. Further cross-linking with factor XIIIa leads to a stable thrombus.

General information
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The plasma concentration of fibrin is 160-350 mg/dl. The fibrin concentration is lower in the lymphatic fluid. The half-life of fibrin is three to five days.

The fibrinogen is elevated as an acute phase protein in acute and chronic inflammation, pregnancy, tumours and occlusive diseases. It is decreased in liver damage, in the context of a consumption coagulopathy or under fibrinolytic therapy.
The fibrin cleavage products polymerize to fibrin, which joins the platelets to a thrombus by attaching them to their GPIIb-/ GPIIIa receptors.

It has long been known that increased fibrinogen levels are a risk factor for the development of arteriosclerotic changes. Fibrinogen correlates with other risk factors such as coronary heart disease, obesity, nicotine, diabetes and cholesterol. Pre-menopausal women and women who take hormonal anti-conception drugs have increased fibrinogen levels.

Regular physical exercise can significantly reduce an elevated fibrinogen level and thus significantly reduce the risk of developing arteriosclerosis. People with low fibrinogen concentrations have a significantly lower risk of developing conorrheal disease, even if they have elevated serum cholesterol.

Standard value: The standard value is 150 to 400 mg/dl; 4.8 - 12.0 ┬Ámol/l

Pathologically decreased: cachexia, medimant, hyperfibrinolysis, congenital A-, hypo- and dysfibrinogenemias, severe liver parenchyma damage, consumption and loss coagulopathy

Pathologically increased: nephrotic syndrome, infections, inflammatory and rheumatic diseases, malignant tumours, necrosis and tissue damage

Note(s)
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The factor I, the fibrinogen, was discovered by Dennis de Commercy and Olof Hammarsten.

Literature
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  1. HA Neumann (2014) The coagulation system. ABW-Wissenschaftsverlag GmbH Berlin S. 49f.

Outgoing links (1)

Prothrombin;

Authors

Last updated on: 29.10.2020