Antithrombin Deficiency

(See also Overview of Thrombotic Disorders Overview of Thrombotic Disorders In healthy people, homeostatic balance exists between procoagulant (clotting) forces and anticoagulant and fibrinolytic forces. Numerous genetic, acquired, and environmental factors can tip... read more .)

Antithrombin is a plasma protein that inhibits thrombin and factors Xa, IXa, and XIa, thereby inhibiting thrombosis.

Heterozygous deficiency of antithrombin has a prevalence of about 0.2 to 0.4%; about half of people affected develop venous thromboses Deep Venous Thrombosis (DVT) Deep venous thrombosis (DVT) is clotting of blood in a deep vein of an extremity (usually calf or thigh) or the pelvis. DVT is the primary cause of pulmonary embolism. DVT results from conditions... read more . Homozygous deficiency is probably lethal to the fetus in utero.

Acquired deficiencies occur in patients with disseminated intravascular coagulation Disseminated Intravascular Coagulation (DIC) Disseminated intravascular coagulation (DIC) involves abnormal, excessive generation of thrombin and fibrin in the circulating blood. During the process, increased platelet aggregation and coagulation... read more , liver disease, or nephrotic syndrome Overview of Nephrotic Syndrome Nephrotic syndrome is urinary excretion of > 3 g of protein/day due to a glomerular disorder plus edema and hypoalbuminemia. It is more common among children and has both primary and secondary... read more , or during heparin therapy. Heparin exerts its anticoagulant effect by activating antithrombin.

Laboratory testing is done for patients with an unexplained blood clot and involves quantification of the capacity of patient plasma to inhibit thrombin in the presence of heparin.