Normal blood coagulation is a complex process involving as many as 20 different plasma proteins, which are known as blood coagulation factors. A series of complex chemical reactions using these factors takes place very rapidly to form an insoluble protein called fibrin that stops bleeding. When certain coagulation factors are deficient or missing, the chain reaction does not take place normally. In this disorder, bleeding ranges from mild to severe.

A congenital factor II deficiency is a very rare inherited disorder that results in deficient blood clotting. It is inherited as an autosomal recessive trait (both parents are carriers). A family history of a bleeding disorder is a risk factor.

Acquired factor II deficiency is common and results from vitamin K deficiency, severe liver disease, and therapeutic use of anticoagulant drugs. Risk factors for vitamin K deficiency are prolonged use of antibiotics, bile duct obstruction, and intestinal malabsorption (inadequate absorption of nutrients from the intestinal tract) disorders. Some newborns are born with vitamin K deficiency.