Fibrinogen, also known as factor I, is a blood clotting protein produced by the liver. This test measures the amount of fibrinogen antigen in the blood which is typically used to evaluate various bleeding and clotting disorders. Low fibrinogen levels can cause excessive bleeding and can be inherited or acquired due to liver disease, kidney disease, or conditions like disseminated intravascular coagulation (DIC). High fibrinogen levels may be caused by inflammation, tissue damage, or infection. Levels may also be elevated in smokers, during pregnancy, and in women taking oral contraceptives. This test is commonly ordered for unexplained bleeding, abnormal clotting test results, or when monitoring the effectiveness of thrombolytic therapy or to evaluate dysfibrinogenemia where fibrinogen is defective.