Factor II (Prothrombin) Deficiency
Factor II (FII) deficiency, also called prothrombin deficiency, was first identified in 1947 by Dr. Armand Quick. The incidence is estimated at 1 in 2 million in the general population. Factor II deficiency is inherited in an autosomal recessive fashion, meaning that both parents must carry the gene to pass it on to their children; it affects men and women equally.
Prothrombin is a precursor to thrombin, an enzyme that converts fibrinogen into fibrin to strengthen a clot. Dysprothrombinemia results when there is an abnormality in the structure of prothrombin. Hypoprothrombinemia occurs when the body doesn’t produce enough prothrombin. Symptoms include excessive umbilical cord bleeding, easy bruising, frequent nosebleeds and hemorrhaging after surgery or trauma. Women with FII deficiency experience menorrhagia, heavy menstrual bleeding, and postpartum hemorrhage after childbirth. Joint bleeding is uncommon.
Diagnosis 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 near or at 50% of normal have little to no bleeding problems. Inherited FII deficiency must be distinguished from the acquired form. Acquired FII deficiency is caused by several factors: long-term use of antibiotics, bile obstruction, impaired absorption of vitamin K from the intestines and severe liver disease. It is more common than the inherited form.
Treatment to control bleeding is achieved using prothrombin complex concentrates (PCCs) or fresh frozen plasma (FFP). PCCs differ in the amount of FII they contain depending on the manufacturer, which complicates treatment. Because PCCs can increase the risk of blood clots, they are typically only prescribed for surgery or after trauma.