Thrombin converts soluble fibrinogen into insoluble fibrin, which when cross-linked becomes the fibrin clot as the last step in the coagulation cascade. Fibrinogen is an acute-phase reactant protein in that the concentration rises sharply in response to many different physiological stimuli such as tissue inflammation or injury. High fibrinogen levels are associated with atherosclerotic cardiovascular disease and with the occurrence of myocardial infarction and stroke.

Other conditions in which fibrinogen is elevated are cancers of the stomach, breast, or kidney, and inflammatory disorders like rheumatoid arthritis. Reduced fibrinogen levels are prevalent in liver disease, prostate cancer, lung disease, bone marrow lesions, malnourishment, and disseminated intravascular coagulation. Other conditions of deficient fibrinogen are congenital afibrinogenaemia, hypofibrinogenaemia, and dysfibrinogenaemia.

The Biorex Diagnostics Fibrinogen reagent is an in vitro diagnostic assay intended for quantitative determination of fibrinogen in plasma.