Definition of Idiopathic aplastic anemia:

Idiopathic aplastic anemia is failure of the bone marrow to properly make blood cells.

See also:

• Anemia
• Secondary (acquired) aplastic anemia

Causes, incidence, and risk factors:

Bone marrow is the soft tissue in the center of bones. It helps form blood cells.

Aplastic anemia results from injury to the blood stem cell, a cell that develops into other blood cell types. The injury causes a reduction in the number of every type of blood cell in the body -- red cells, white cells, and platelets. Low numbers of red cells, white cells, and platelets is a condition called pancytopenia.

Idiopathic means the cause is unknown. However, idiopathic aplastic anemia is thought to occur when the body reacts against its own cells. This is called an autoimmune disorder.

The disease may be acute or chronic, and may get worse over time. There are no known risk factors.

Aplastic anemia may also be caused by certain medical conditions (such as pregnancy or lupus) or exposure to some toxins or drugs (including chemotherapy). See: Secondary (acquired) aplastic anemia

In some cases, aplastic anemia is associated with another blood disorder called paroxysmal nocturnal hemoglobinuria (PNH).