86 Fibrinogen

Fibrinogen: clotting factor I and acute-phase protein, normal range, causes of low and high levels.

Fibrinogen (coagulation factor I) is a large protein made by the liver. At the end of the coagulation cascade, thrombin converts soluble fibrinogen into fibrin threads. These cross-link into a net that, together with platelets, forms a stable clot. Fibrinogen is also an acute-phase protein: its level rises with inflammation, infection, tissue injury, pregnancy and smoking. Both too little and too much are harmful: low fibrinogen causes bleeding, high fibrinogen is associated with cardiovascular disease.

CoagulationAcute phaseBleeding

Adults≈ 2–4 g/L (200–400 mg/dL)

Bleeding risk< 1.5 g/L

Severe deficiency< 1.0 g/L

MethodClauss (functional)

Figure 1. Plasma fibrinogen zones (Clauss method). In major bleeding, guidelines recommend fibrinogen replacement at levels of about 1.5 g/L or lower.

Low fibrinogen

Consumption: disseminated intravascular coagulation (DIC), major bleeding and trauma, obstetric haemorrhage (placental abruption, amniotic fluid embolism)
Dilution after large-volume transfusion or fluids
Reduced production: advanced liver disease, severe malnutrition
Medicines: thrombolysis, asparaginase, valproate
Inherited: afibrinogenaemia, hypofibrinogenaemia, dysfibrinogenaemia (abnormal function)

High fibrinogen

Raised levels occur with infections, inflammatory diseases (rheumatoid arthritis, vasculitis), cancer, after surgery or myocardial infarction, in pregnancy, with oral contraceptives, smoking, obesity and diabetes. In a meta-analysis of 31 prospective studies (154 211 participants), higher fibrinogen was associated with higher risk of coronary heart disease and stroke. Whether this link is causal is not established.

Seek emergency care

for heavy or uncontrolled bleeding, especially after childbirth, injury or surgery. A rapidly falling fibrinogen in these situations needs urgent treatment.

References

Rossaint R, Afshari A, Bouillon B, et al. The European guideline on management of major bleeding and coagulopathy following trauma: sixth edition. Crit Care. 2023;27(1):80. doi:10.1186/s13054-023-04327-7
Fibrinogen Studies Collaboration. Plasma fibrinogen level and the risk of major cardiovascular diseases and nonvascular mortality: an individual participant meta-analysis. JAMA. 2005;294(14):1799–1809. doi:10.1001/jama.294.14.1799
Hoffman M, Monroe DM. A cell-based model of hemostasis. Thromb Haemost. 2001;85(6):958–965. doi:10.1055/s-0037-1615947

This article is for general information and does not replace a consultation with a doctor. Laboratory results must be interpreted by a physician together with symptoms and other tests.

Published on 30 April 2024