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a soluble protein, a globulin, in blood plasma, converted to fibrin by the action of the enzyme thrombin when blood clots
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005


The major clot-forming substrate in the blood plasma of vertebrates. Though fibrinogen represents a small fraction of plasma proteins (normal human plasma has a fibrinogen content of 2–4 mg/ml of a total of 70 mg protein/ml), its conversion to fibrin causes a gelation which blocks the flow of blood. Upon injury, sufficient amounts of the clotting enzyme, thrombin, are generated in about 5 min clotting time to produce a gel. Although clotting in the circulation (thrombosis) can be extremely dangerous, clotting is an essential and normal response for preventing the loss of blood. Individuals born with the hereditary absence of fibrinogen (afibrinogenemia) suffer from severe bleeding, which can be counteracted by transfusing normal plasma or purified fibrinogen.

Fibrinogen is synthesized by the hepatocytes in the liver, and the synthetic rate can be stimulated by hormones. Significant amounts of carbohydrates become attached to the protein before it is secreted into the circulation; alterations in its carbohydrate composition as found in some liver diseases can give rise to abnormal fibrinogens with defective clotting properties.

Clotting is regulated by two enzymes, thrombin and factor XIIIa (fibrinoligase, activated fibrin-stabilizing factor, transglutaminase). Thrombin exerts a dual control by regulating the rate of fibrin formation as well as producing factor XIIIa. In the plasma milieu, the fibrin molecules readily aggregate into a clot. In order to obtain a clot structure of a strength sufficient to stem bleeding, however, it is necessary for the thrombin-modified factor XIII to be activated to XIIIa. Factor XIIIa acts as a transamidating enzyme which strengthens the fibrin clot by creating cross-links between the molecules. Without such cross-links, a clot structure would be like a brick wall without mortar. Individuals with the hereditary absence of factor XIII often suffer from severe bleeding, even though their clotting times are in the normal range. See Blood, Immunoglobulin

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a soluble plasma protein belonging to the globulin class; coagulation factor I, which is converted to fibrin by the action of the enzyme thrombin. Molecular weight, approximately 350,000.

The fibrinogen molecule is globular, with a diameter of about 22 nanometers. It consists of two identical subunits, each of which is formed of three dissimilar polypeptide chains designated α, β, and γ, where α and β are peptides split off by the action of thrombin. Fibrinogen is synthesized in the parenchymatous cells of the liver. Its concentration in human plasma is 300–500 mg per 100 milliliters. A hemorrhagic diathesis occurs as a result of fibrinogen insufficiency or the formation of molecules with an anomalous structure.

Fibrinogen obtained by precipitation with ethyl alcohol from plasma is used to arrest bleeding during surgery, in obstetrical and gynecological practice, and in cases of hemophilia and diseases associated with low blood fibrinogen levels. Fibrinogen preparations are also produced for laboratory research. Fibrinogen derived from human blood is used clinically.


Andreenko, G. V. “Sovremennye dannye o khimii i fiziologii fibrinogena.” Uspekhi sovremennoi biologii, 1974, vol. 77, issue 1.
“Models Proposed for the Fibrinogen Molecule and for the Polymerization Process.” Thrombosis Research, 1975, vol. 6.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


A plasma protein synthesized by the parenchymal cells of the liver; the precursor of fibrin. Also known as factor I.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
"We discovered that fibrinogen accumulates within the remaining liver quickly after surgery and tells platelets to act as first responders, triggering the earliest phase of regeneration," said James Luyendyk, a professor of pathobiology in the College of Veterinary Medicine.
Researchers suggest that these findings could lead to new treatments that would help doctors correct low levels of the protein by using fibrinogen concentrates that can be administered during surgery.
The aim of this study was to examine whether the postprocedural change in CRP and fibrinogen levels was associated with the extent of periprocedural arterial injury measured by percutaneous transluminal angioplasty (PTA) treated segment length, balloon inflation time and stented segment length.
HITACHI 7600 automatic biochemical analyzer was used to detect the levels of Total Cholesterol (TC), High Density Lipoprotein (HDL), Low Density Lipoprotein (LDL), Triglyceride (TG) and fibrinogen, together with platelet and leukocyte counts.
Compared to AWMTA, samples exposed to EB showed an increased quantity of fibrinogen; however, these results were not statistically significant (P>0.05) (Table 2).
Multivariable linear regression analysis was performed with TEG-MA as the dependent variable and diabetes mellitus as the covariate with forward stepwise adjustment for remaining clinical variables and fibrinogen level.
Among them, laboratory parameters including fibrinogen, high-density lipoprotein-cholesterol (HDL-C), low-density lipoprotein-cholesterol (LDL-C), total cholesterol (TC), triglyceride (TG), and HbA1c were subsequently analyzed by an automated analyzer (Abbott AxSYM, Park, IL).
Patients were screened for bleeding diathesis by the following tests- platelet count, peripheral smear, PT, aPTT, D-dimer and Fibrinogen irrespective of the presence of clinical bleeding.
Elevated inflammatory biomarkers [C-reactive protein (CRP), fibrinogen and white blood cells (WBC)] in patients with COPD are related to increased exacerbations risk, even among patients with a mild form of COPD and those without previous exacerbations (5).
It is initiated as thrombin proteolytically removes fibrinopeptide A from the central E region of fibrinogen, thus converting fibrinogen to desA fibrin.

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