Antithrombin III
Antithrombin III is a natural protein that helps keep your blood from clotting too much by slowing the clotting process. A blood test measures its level or activity.
Antithrombin helps maintain the balance between clotting and bleeding, so measuring it can help explain a tendency to form clots. It is often checked when investigating unexplained or repeated clots. It is interpreted alongside other tests that assess clotting risk.
A high antithrombin level is generally not considered a health concern and rarely needs action. It is not typically associated with a specific problem. Your clinician will interpret it in the context of why the test was done.
A low antithrombin level can be associated with a greater tendency to form clots and may be inherited or acquired. Your clinician will use additional testing to interpret a low result.
A value within the normal range supports balanced clotting regulation. Your clinician will interpret your result based on your personal and family clotting history.
Sources
Educational context only, not medical advice or a diagnosis. Reference ranges vary by lab, age and sex; always discuss your results with a clinician.