Factor II Deficiency

(Also known as Prothrombin Deficiency)

Factor II deficiency is quite rare, with only 26 cases reported in the medical literature. The incidence is estimated at 1 in 2 million. It is inherited in an autosomal recessive fashion, which means it affects men and women equally.

Prothrombin is a precursor to thrombin, which converts fibrinogen into fibrin. Fibrin, in turn, strengthens a protective clot. Factor II deficiency usually takes the form of an abnormality in the structure of prothrombin rather than a lack of the protein itself.


People with a more severe Factor II deficiency have:

  • Severe bruising
  • Bleeding from the nose and mouth
  • Menorrhagia, as well as muscle bleeds, head bleeds and bleeding after trauma; joint bleeding is rare


Diagnosis for factor II deficiency is made with a Prothrombin Time (PT) Test and an Activated Partial Thromboplastin Time (aPTT) Test. Levels of prothrombin deficiency can range from 2% to 50% of normal. Patients with levels reaching 50% of normal have little to no bleeding problems. The inherited condition must be distinguished from the acquired form of Factor II, which is also associated with bleeding. Hereditary Factor II deficiency has also been reported as part of a combined disorder with factor VII, IX, X and protein C and S.


Treatment varies in these rare disorders.