Liver diseases and hemostasis.

The liver prays a key role in the regulation of hemostasis. By producing mo st clotting factors and inhibitors, as well as a number of the proteins inv olved in fibrinolysis, and by clearing from the bloodstream activated enzym es involved in clotting or fibrinolysis, the liver protects against both bl eeding and undue activation of coagulation. It follows that liver diseases are commonly responsible for hemostasis abnormalities including decreased p roduction of clotting factors, thrombocytopenia, platelet dysfunction, and increased circulating fibrinolytic activity. With the exception of cholesta sis and in the absence of a specific setting such as pregnancy, the abnorma lities are the same in all liver diseases, and their severity varies only w ith the degree of hepatocellular failure. Although liver diseases do not di rectly cause disseminated intravascular coagulation (DIC), they are a major risk factor for DIC in patients with infection or shock, as well as during pregnancy. In patients with liver diseases, hemostasis tests can be requir ed to evaluate the degree of hepatocellular failure, the severity of hemost asis disorders manifesting as bleeding, or the bleeding risk before an inva sive procedure. Prothrombin time determination is usually sufficient to eva luate the degree of hepatocellular failure, although in some cases assays o f fibrinogen and factors II, VII, X, V are also useful. Evaluation of the b leeding risk prior to an invasive procedure requires a study of platelet fu nction and measurement of circulating fibrinolytic activity, which is parti cularly likely to be abnormal in patients with severe hepatocellular failur e and/or alcohol abuse. A less common reason for investigating hemostasis i s a search for the cause of a thrombotic condition, such as portal vein thr ombosis or Budd-Chiari syndrome.