Paroxysmal nocturnal hemoglobinuria
Paroxysmal nocturnal hemoglobinuria (PNH) is a rare disease characterised by hemolytic anemia, thrombosis and red urine due to breakdown of red blood cells. PNH is the only hemolytic anemia caused by an acquired intrinsic defect in the cell membrane. more...
Signs and symptoms
Quite paradoxically, the destruction of red blood cells (hemolysis) is neither paroxysmal or nocturnal the majority of the time (this constellation of symptoms is seen in only 25% of patients). On-going hemolysis is a more common characteristic.
A common finding in PNH is the presence of breakdown products of RBCs (hemoglobin and hemosiderin) in the urine.
An inconsistent, but potentially life-threatening, complication of PNH is the development of clot in the veins (venous thrombosis). These clots (thrombi) are often found in the hepatic (causing Budd-Chiari syndrome), portal (causing portal vein thrombosis), and cerebral veins (causing cerebral venous thrombosis).
Many patients with bone marrow failure (aplastic anemia) develop PNH (10-33%). Aplastic anemia can be caused by an attack by the immune system against the bone marrow. For this reason, drugs that suppress the immune system are being researched as a therapy for PNH.
A sugar or sucrose lysis test, in which a patient's red blood cells are placed in low ionic strength solution and observed for hemolysis, is used for screening. A more specific test for PNH, called Ham's acid hemolysis test, is performed if the sugar test is positive for hemolysis.
Modern methods include flow cytometry for CD55, CD16 and CD59 on white and red blood cells. Dependent on the presence of these molecules on the cell surface, they are classified as type I, II or III PNH cells.
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