 Heparin @-@ induced thrombocytopenia ( HIT ) is due to an immune system reaction against the anticoagulant drug heparin ( or its derivatives ) . Though it is named for associated low platelet counts , HIT is strongly associated with risk of venous and arterial thrombosis . Paroxysmal nocturnal hemoglobinuria ( PNH ) is a rare condition resulting from acquired alterations in the PIGA gene , which plays a role in the protection of blood cells from the complement system . PNH increases the risk of venous thrombosis but is also associated with hemolytic anemia ( anemia resulting from destruction of red blood cells ) . Both HIT and PNH require particular treatment . 
