Fibrinogen is a soluble plasma protein (coagulation factor I) synthesized by hepatocytes that serves as the precursor to fibrin, the structural protein of blood clots. During hemostasis, thrombin cleaves fibrinogen into fibrin monomers which polymerize to form the clot matrix. Fibrinogen is also an acute phase protein, increasing 2-10 fold during inflammation. Elevated fibrinogen contributes to cardiovascular disease risk by promoting thrombosis and increasing blood viscosity.
Fibrinogen is a large glycoprotein (340 kDa) consisting of two sets of three polypeptide chains (AΞ±, BΞ², Ξ³). It circulates at 2-4 g/L in healthy individuals. When tissue injury occurs, the coagulation cascade is activated, culminating in thrombin generation. Thrombin cleaves fibrinopeptides A and B from fibrinogen, converting it to fibrin monomers. These monomers spontaneously polymerize through hydrogen bonds, forming protofibrils that laterally aggregate into fibrin fibers. Factor XIIIa cross-links fibrin polymers via covalent bonds, stabilizing the clot. During inflammation, IL-6 and other cytokines stimulate hepatic fibrinogen synthesis (acute phase response). Elevated fibrinogen increases blood viscosity, erythrocyte aggregation (rouleaux formation), and thrombotic risk. Fibrinogen also binds to platelet GPIIb/IIIa receptors, promoting platelet aggregation.
Elevated fibrinogen is an independent risk factor for cardiovascular disease, stroke, and peripheral artery disease. It increases with chronic inflammation, smoking, obesity, diabetes, and stress. Fibrinogen levels >4 g/L are associated with doubled cardiovascular risk. The mechanism involves increased clot formation, blood viscosity, and inflammatory signaling. Fibrinogen also reflects systemic inflammation intensity β a useful biomarker in cPNI practice. Interventions to reduce fibrinogen include anti-inflammatory diet, omega-3 fatty acids, exercise, stress reduction, and smoking cessation.
- Normal range 2-4 g/L; >4 g/L indicates elevated cardiovascular risk
- Increases 2-10 fold during acute phase response
- Half-life ~4 days; levels reflect recent inflammatory state
- Cleaved by thrombin into fibrin monomers forming clot matrix
- IL-6 is primary cytokine stimulating hepatic fibrinogen synthesis
- Elevated fibrinogen increases blood viscosity and erythrocyte aggregation
- Strong predictor of cardiovascular events independent of other risk factors
- thrombin β thrombin cleaves fibrinogen into fibrin initiating clot formation
- fibrin β fibrin is polymerized form of fibrinogen creating clot structure
- acute phase protein β fibrinogen is major acute phase protein increasing during inflammation
- IL-6 β IL-6 stimulates hepatic fibrinogen synthesis during inflammation
- inflammation β chronic inflammation elevates fibrinogen increasing thrombotic risk
- CRP β fibrinogen and CRP often correlate as acute phase proteins
- cardiovascular disease β elevated fibrinogen is independent risk factor for CVD
- coagulation β fibrinogen is central protein in coagulation cascade
- wound healing β fibrinogen forms provisional matrix for wound repair
- blood viscosity β elevated fibrinogen increases blood viscosity impairing circulation
- rouleaux formation β high fibrinogen causes RBC aggregation (rouleaux) visible on dark-field microscopy
- platelets β fibrinogen binds platelet receptors promoting aggregation
- liver β liver synthesizes fibrinogen in response to inflammatory cytokines
- chronic stress β chronic stress elevates fibrinogen through sustained inflammation and cortisol
- smoking β smoking increases fibrinogen levels contributing to thrombotic risk
- omega-3 fatty acids β omega-3s reduce fibrinogen levels through anti-inflammatory effects
- exercise β regular exercise reduces fibrinogen levels
- obesity β obesity elevates fibrinogen through chronic inflammation
- diabetes β diabetes increases fibrinogen contributing to vascular complications
- loneliness β chronic loneliness elevates inflammatory markers including fibrinogen
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