(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 0.02 to 0.2% (1 General reference Because antithrombin inhibits thrombin and factors Xa, IXa, and XIa, deficiency of antithrombin predisposes to venous thrombosis. (See also Overview of Thrombotic Disorders.) Antithrombin is... read more ); 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.
Diagnosis of Antithrombin Deficiency
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. Heparin normally inhibits coagulation by accelerating inactivation of thrombin by antithrombin. In patients with antithrombin deficiency, inactivation of thrombin is reduced. The residual thrombin in the test mixture is inversely proportional to the functional antithrombin concentration in the patient's plasma. Antithrombin protein levels also can be measured with immunologic assays, but these tests only measure the amount of antithrombin protein in the sample and cannot assess the function of this protein. Since rare patients with antithrombin deficiency express dysfunctional antithrombin proteins, activity assays are favored over antigen assays for the diagnosis of antithrombin deficiency.
Treatment of Antithrombin Deficiency
Direct oral anticoagulants or warfarin can be used for long-term anticoagulation in patients with antithrombin deficiency and venous thromboembolism (1, 2 Treatment references Because antithrombin inhibits thrombin and factors Xa, IXa, and XIa, deficiency of antithrombin predisposes to venous thrombosis. (See also Overview of Thrombotic Disorders.) Antithrombin is... read more ).
1. Campello E, Spiezia L, Simion C, et al. Direct Oral Anticoagulants in Patients With Inherited Thrombophilia and Venous Thromboembolism: A Prospective Cohort Study. J Am Heart Assoc 2020;9(23):e018917. doi:10.1161/JAHA.120.018917
2. Pabinger I, Thaler J. How I treat patients with hereditary antithrombin deficiency. Blood 2019;134(26):2346-2353. doi:10.1182/blood.2019002927
Drugs Mentioned In This Article
|Hepflush-10 , Hep-Lock, Hep-Lock U/P, Monoject Prefill Advanced Heparin Lock Flush, SASH Normal Saline and Heparin