What is this test?
Antithrombin is a natural anticoagulant that helps control thrombin and other clotting enzymes. Testing is used selectively to investigate inherited or acquired antithrombin deficiency.
Why might it be ordered?
- During specialist assessment after an unusual or recurrent blood clot.
- To investigate reduced response to heparin or selected family history.
What sample is needed?
A blood sample is required. The laboratory chooses the correct tube and handles the sample for this test.
How should you prepare?
The test may take several working days, and the laboratory may request fasting; confirm before attending. Acute thrombosis, heparin, liver disease and protein loss can alter the result. Do not stop anticoagulants without medical instructions.
How should you understand the result?
A low result can be inherited or acquired and usually needs confirmation at an appropriate time. Activity and antigen assays provide different information.
Sources and editorial status
This patient-facing text is an editorial draft. It should be approved by a laboratory physician before official publication.