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Antithrombin



Why Get Tested

To help investigate the cause of recurrent inappropriate blood clotting to help diagnose an antithrombin deficiency

When To Get Tested

A couple of months after getting a blood clot thrombotic episode or when you are not responding as expected to heparin anticoagulation therapy

Sample Required

A blood sample drawn from a vein in your arm

Test Preparation Needed

None




Common Questions


Antithrombin testing is primarily ordered along with other tests for excessive clotting disorders to investigate the cause of recurrent blood clot formation thrombosis Testing evaluates the activity function and the amount quantity of antithrombin and helps identify antithrombin deficiency The activity test is performed first to evaluate whether the total amount of functional antithrombin is normal If the antithrombin activity is low then the antithrombin antigen test is performed to determine the quantity of antithrombin present These two tests can be used to differentiate between type 1 and type 2 antithrombin deficiencies If a deficiency is detected both antithrombin tests are typically repeated at a later date to confirm test findings Antithrombin testing may sometimes be used to evaluate people who are not responding as expected to heparin Heparin is an anticoagulant drug that is given to people who have a blood clot or are at an increased risk of forming inappropriate blood clots The effects of heparin are mediated by antithrombin Heparin can greatly increase antithrombin activity thus inhibiting formation of blood clots but those who are antithrombin-deficient are resistant to heparin treatment

Antithrombin activity testing is ordered along with other tests for excessive clotting disorders such as protein C and protein S and lupus anticoagulant when a person has been experiencing recurrent blood clots Antithrombin testing should be performed to evaluate an individual for an excessive clotting disorder only after a blood clot has been treated and resolved as both the presence of the clot and the therapy used to treat it will affect antithrombin results Antithrombin testing may also be ordered when a person is not responding as expected to heparin anticoagulation when unusually high doses of heparin are necessary to achieve the desired level of anticoagulation

Decreased antithrombin activity and decreased quantities of antithrombin antigen suggest a type 1 antithrombin deficiency In this case the activity is decreased because there is less antithrombin available to participate in clotting regulation Reduced antithrombin activity and normal levels of antithrombin antigen suggest a type 2 antithrombin deficiency This means that there is sufficient antithrombin protein but it is not functioning as it should In either case a deficiency increases the affected person s risk of developing an inappropriate blood clot If the antithrombin activity is normal then the antithrombin antigen test is usually not performed In this case the antithrombin is functioning adequately and the recurrent thrombotic episodes being investigated are likely due to a cause other than an antithrombin deficiency Temporarily or chronically decreased antithrombin levels may be seen with conditions that affect its consumption or production such as DIC disseminated intravascular coagulation an acute or chronic condition characterized by the consumption of clotting factors an affected person may bleed and or clot DVT deep vein thrombosis a blood clot usually in a deep leg vein Liver disease Nephrotic syndrome Protein-losing condition Pulmonary embolism Heparin therapy temporary lower antithrombin level Infants during the first few days of life about 50 of healthy adult level Estrogen therapy Increased levels of antithrombin are not usually considered a problem

If a person with an antithrombin deficiency also has other coagulation risks such as a protein C or S deficiency a factor V leiden mutation or oral contraceptive use then the person may be at a significantly elevated risk of developing a blood clot Antithrombin deficiency can increase the risk of recurrent miscarriage People with antithrombin deficiency may need preventive anticoagulation therapy prior to medical or surgical procedures Antithrombin concentrates and recombinant antithrombin are now available as a medication to temporarily correct acute or chronic antithrombin deficiencies

If you have a personal or strong family history of recurrent blood clots your healthcare provider may perform an examination to determine your general state of health and order a series of tests to determine your risk of having an excessive clotting disorder The more inherited or acquired risk factors you have such as a factor V leiden or PT 20210 mutation or a protein C or S deficiency the higher your relative risk of clotting This risk can be further increased if you are overweight sedentary have hypertension smoke and or take oral contraceptives It is important to remember however that any overall relative risk that is determined is still a statistical risk No one can predict whether a particular person will actually experience recurrent clotting

Yes This is important information that your healthcare providers should know about as it affects your body s ability to clot appropriately during and after a medical procedure

In general no If you have an acquired deficiency that is related to an underlying condition such as liver disease then treating the condition may ease or eliminate the deficiency If needed your healthcare provider may treat you with antithrombin as a medication to temporarily correct the deficiency