Ministry Health Care

Congenital antithrombin III deficiency is a genetic disorder that causes the blood to clot more than normal.

Deficiency - antithrombin III - congenital; Antithrombin III deficiency - congenital

Antithrombin III is a protein in the blood that naturally blocks blood clots from forming. Congenital antithrombin III deficiency is an inherited disease. It occurs when a person receives one abnormal copy of a gene from a parent with the disease.

The abnormal gene leads to low levels of antithrombin III. These low levels of antithrombin III can cause abnormal blood clots (thrombi) that may damage organs.

Often, patients with this condition will have a blood clot at a young age and will have a family member who has also experienced a blood clotting episode. In people with this condition, a blood clot may occur without the common risk factors of pregnancy, lack of movement (due to surgery or trauma), or use of oral birth control pills.

Patients will usually have symptoms of a blood clot, including:

• Coughing up blood
• Fainting
• Shortness of breath and pain when taking deep breaths
• Swelling of one leg

A physical examination may show:

• Abnormal lung sounds
• Fast breathing
• Fast heart rate
• Swollen foot or leg

The diagnosis is made by checking for low levels of antithrombin III in the patient's blood. There are several techniques for checking these levels.

A blood clot is treated with blood thinning medications (also called anticoagulants). How long you need to take these medications depends on how serious the blood clot was and other factors. Discuss this with your health care provider.

Most patients have a good outcome if they stay on anticoagulant medications.

Blood clots can cause death, especially if they are in the lungs.

See your health care provider if you have symptoms of this condition.

Because this is an inherited condition, there is no way to prevent it. However, once a patient is diagnosed with antithrombin III deficiency, all close family members should be screened.

Bauer KA. Hypercoagulable states. In: Hoffman R, Benz EJ Jr., Shattil SJ, et al, eds. Hoffman Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Churchill Livingston Elsevier;2008:chap 134.

Schafer A. Thrombotic disorders: Hypercoagulable states. In: Goldman L, Ausiello D. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 182.