Lab marker · Low

Low Antithrombin III: what it means

A Antithrombin III result below the normal range is considered low. Here is what a reduced Antithrombin III can point to, and when it is worth discussing with a doctor.

Reference range: ~80–120% of normal activity; a natural anticoagulant that keeps clotting in check — a LOW level (deficiency) is a thrombophilia, raising the risk of abnormal blood clots (thrombosis)

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What a low Antithrombin III can mean

  • Inherited antithrombin deficiency — a genetic thrombophilia, one of the stronger inherited clotting risks.
  • Liver disease — less antithrombin is made.
  • Kidney disease (nephrotic syndrome) — protein is lost in the urine.
  • Active clotting or DIC — antithrombin is consumed.
  • Heparin resistance — low antithrombin blunts heparin's effect.

When to discuss with a doctor

Antithrombin is a specialist test, part of a thrombophilia work-up rather than a routine check. It is measured mainly when someone has had a blood clot that is unexplained, unusually severe, recurrent, in an unusual site, or at a young age, or when there is a strong family history — to look for an inherited tendency to clot. A confirmed antithrombin deficiency influences how a clot is treated and prevented, decisions about longer-term anticoagulation, and guidance for family members. Because an acute clot and blood thinners themselves lower the level, timing and interpretation are important and best handled by a haematologist. Mediora.AI shows antithrombin alongside protein C, protein S and D-dimer so the thrombophilia pattern is read together; confirming and acting on a deficiency belongs with your doctor or haematologist.

Conditions this can relate to

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Mediora.AI is informational - interpretation, not a diagnosis. A single out-of-range value is common and often benign; always discuss decisions with your doctor.