Paroxysmal nocturnal hemoglobinuria (PNH), sometimes referre to as Marchiafava-Micheli syndrome, is a rare, acquired, potentially life-threatening disease of the blood characterised by complement-induced hemolytic anemia (anemia due to destruction of red blood cells in the bloodstream), red urine (due to the appearance of hemoglobin in the urine) and thrombosis. PNH is the only hemolytic anemia caused by an acquired (rather than inherited) intrinsic defect in the cell membrane (deficiency of glycophosphatidylinositol leading to absence of protective proteins on the membrane). It may develop on its own ("primary PNH") or in the context of other bone marrow disorders such as aplastic anemia ("secondary PNH").