What is Fibrinogen Level?

Also Known As: Factor I Assay, Fibrinogen Activity (Functional), Fibrinogen Antigen, Cardiac Fibrinogen

Fibrinogen is a protein, specifically a clotting factor (factor I), that is essential for proper blood clot formation. Two types of tests are available to evaluate fibrinogen. A fibrinogen activity test evaluates how well fibrinogen functions in helping to form a blood clot. A fibrinogen antigen test measures the amount of fibrinogen in the blood.

Fibrinogen is produced by the liver and released into the blood along with several other clotting factors (also called coagulation factors). Normally, when a body tissue or blood vessel wall is injured, a process called hemostasis begins to help stop the bleeding by forming a plug at the injury site. Small cellular fragments called platelets to clump and stick to the injury site and clotting factors are activated one after the other. This last part is called the coagulation cascade.

As the cascade nears completion, soluble fibrinogen is converted into insoluble fibrin threads. These threads then crosslink together to form a fibrin net that stabilizes at the injury site. The fibrin net adheres to the site of injury along with the platelets to form a stable blood clot. This barrier prevents additional blood loss and remains in place until the injured area is healed.

For a stable clot to form, there must be enough normally functioning platelets and coagulation factors. Too little, too much, or dysfunctional clotting factors or platelets can lead to bleeding episodes and/or to the formation of an inappropriate blood clot (thrombosis). Several laboratory tests, including fibrinogen tests, can be used to evaluate the clotting process. Fibrinogen testing includes:

• A fibrinogen activity test evaluates that part of the clotting process in which soluble fibrinogen is converted into fibrin threads. It measures the time that it takes for a fibrin clot to form after a standard amount of thrombin is added to your blood sample (plasma). The time it takes for a clot to form directly correlates with the amount of active fibrinogen that is present. Prolonged clot-formation times may be due to decreased levels of normal fibrinogen or may be due to fibrinogen that does not function as it should (dysfunctional).
• A fibrinogen antigen test measures the level of fibrinogen in a blood sample, including both functional and dysfunctional fibrinogen.

Fibrinogen is also one of several blood factors that are called acute phase reactants. Blood levels of fibrinogen along with other acute phase reactants rise sharply with conditions causing acute tissue inflammation or damage. Tests for these acute phase reactants, including fibrinogen, may be performed to determine the extent of inflammation in the body.