Test Details: Protein S is a natural anticoagulant i.e. it protects blood from clotting too much. If there is reduced level of protein S then there are more chances of blood clotting. But certain conditions can increase the risk of clot formation such as pregnancy, surgery, infections and extended period of inactivity. Protein S level are done in case of family history of clotting disorder, unexplained thrombosis, history of recurrent miscarriage.