Fibrinogen activity (Clauss)

The final stage in the molecular co-operation of the procoagulant participants of secondary haemostasis is the conversion of soluble fibrinogen monomers to insoluble, cross-linked fibrin polymers to stabilse the blood clot. Fibrinogen is a large, symmetrical dimeric glycoprotein composed of two identical sub-units, each of which is comprised of three non-identical polypeptide chains. It is present in plasma at a high concentration and is also contained in platelet α-granules. Fibrin is formed by thrombin cleavage of the small fibrinopeptides A & B from intact fibrinogen molecules that exposes donor sites which interlock with complementary unshielded acceptor sites on adjacent molecules to promote polymerisation.

Quantitative and qualitative deficiencies of fibrinogen can be congenital or acquired and give rise to bleeding. More rarely, some dysfibrinogenemias can predispose to thrombosis.