 Thrombophilia ( sometimes hypercoagulability or a prothrombotic state ) is an abnormality of blood coagulation that increases the risk of thrombosis ( blood clots in blood vessels ) . Such abnormalities can be identified in 50 % of people who have an episode of thrombosis ( such as deep vein thrombosis in the leg ) that was not provoked by other causes . A significant proportion of the population has a detectable abnormality , but most of these only develop thrombosis in the presence of an additional risk factor . 
