 In thrombophilia , the balance between " procoagulant " and " anticoagulant " activity is disturbed . The severity of the imbalance determines the likelihood that someone develops thrombosis . Even small perturbances of proteins , such as the reduction of antithrombin to only 70 – 80 % of the normal level , can increase the thrombosis risk ; this is in contrast with hemophilia , which only arises if levels of coagulation factors are markedly decreased . 
