Paroxysmal Nocturnal Hemoglobinuria

Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disorder of stem cells and is caused by a gene alteration on the X chromosome. Paroxysmal nocturnal hemoglobinuria is known to be associated with an increased risk of clotting.

Paroxysmal nocturnal hemoglobinuria results in the breakdown of red blood cells, which causes the release of hemoglobin into the blood. Ultimately, the hemoglobin is released into the urine. This release produces dark-colored urine most often in the morning. It is called “nocturnal” because it was believed that the breakdown of red blood cells occurred during sleep, but this belief was later disproved. Hemolysis has been shown to occur throughout the day, but the quantity of urine that occurs during sleep results in the dramatic color change.

Paroxysmal nocturnal hemoglobinuria is an inherited condition related to a genetic change in stem cells. In people with paroxysmal nocturnal hemoglobinuria, surface proteins are missing in the membrane of all blood cells (including platelets as well as red and white blood cells).


This disorder usually presents in adulthood and is less common in childhood. In adults, paroxysmal nocturnal hemoglobinuria is most commonly seen as hemolytic anemia with nighttime episodes, while in children, paroxysmal nocturnal hemoglobinuria is most commonly associated with bone marrow failure.

Blood clots may occur in 39% of adults and 31% of children with paroxysmal nocturnal hemoglobinuria. The clots usually occur in the veins, particularly in the veins of the liver (Budd-Chiari syndrome); however, the portal veins, central nervous system, and peripheral venous system may also be involved. Increased circulating activated platelets have been implicated in clotting events due to paroxysmal nocturnal hemoglobinuria, but no consistent abnormality with clotting has been reported.