Disorder characterized by intravascular hemolysis and hemoglobinuria; some cases occur on exposure to cold and are due to the presence of an autohemolysin in the serum; other cases are more marked during or immediately after sleep and are considered to be due to an acquired intracorpuscular defect.

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare, acquired, life-threatening disease of the blood characterized by destruction of red blood cells by the complement system, a part of the body's innate immune system. This destructive process occurs due to deficiency of the red blood cell surface protein DAF, which normally inhibits such immune reactions...