Other names: Activity and Antigen; ATIII; Functional Antithrombin III

Antithrombin is a protein, which is produced by the liver to regulate blood clotting. Antithrombin is produced to prevent excessive and abnormal clotting.

Why is the test used?

The antithrombin test is used to measure the levels of antithrombin in the blood; the test can be used to diagnose clotting deficiencies and identify problems which are contributing to abnormal clotting on a regular basis.

A doctor will usually advise a patient to have the antithrombin test if they have experienced abnormal clotting; the test is also used to monitor the efficacy of heparin treatment, for those who have already been diagnosed with conditions relating to unsuitable blood clotting.

How is the test performed?

The test is done using a sample of blood, which is collected from a vein in the arm. The doctor or nurse will place a tourniquet on the upper arm to encourage the veins to swell temporarily; this will make it easier for them to insert the needle into a vein. Usually, doctors use a vein on the inside of the elbow. A needle is inserted into the vein and the blood is collected in a syringe. The sample is then bottled and labelled before being sent off to the laboratory for analysis.

What do the test results show?

Decreased levels of antithrombin activity usually indicate a type 1 antithrombin deficiency; this is caused by a lack of antithrombin. If levels are normal but activity is low, this will usually indicate a type 2 deficiency.

Decreased antithrombin levels may be caused by:

  • Liver disease
  • DVT (deep vein thrombosis)
  • DIC (disseminated intravascular coagulation)
  • Pulmonary embolism
  • Nephrotic syndrome

Increased levels of antithrombin are not usually a problem; however, increased levels may be caused by other health conditions, including:

  • Kidney transplant
  • Vitamin K deficiency
  • Acute hepatitis
  • Taking medications such as warfarin

Specific Blood Tests

© Medic8® | All Rights Reserved