Paroxysmal nocturnal hemoglobinuria (PNH)

Alternative names:

PNH

Definition:

A rare, acquired disorder of red blood cells that destroys them, resulting in the presence of hemoglobin in the urine. The disorder is characterized by dark urine in the morning with urine becoming lighter throughout the day.

Causes, incidence, and risk factors:

The exact cause of this rare disorder is unknown. It is thought to be a disorder of the stem cell (the immature form of blood cells) in which a sensitivity to complement (a substance produced by the immune system) occurs in the cell membrane. The disease may affect people of any age, but it is most common in the 30 to 40 age group. Red blood cell, white blood cell and platelet counts may be low. Urine may be red or brown in the morning, signifying the breakdown of red blood cells during the night with release of hemoglobin into the circulation and then the urine. Blood clots may form in some people. The disease may progress to aplastic anemia or acute myelogenous leukemia. Risk factors except for prior aplastic anemia) are unknown. The incidence is 1 out of 100,000 people.