Definition of Idiopathic autoimmune hemolytic anemia:

Idiopathic autoimmune hemolytic anemia is a drop in the number of red blood cells due to a problem with the body's defense (immune) system.

Causes, incidence, and risk factors:

Idiopathic autoimmune hemolytic anemia is an acquired disease that occurs when antibodies form against a person's own red blood cells. In the idiopathic form of this disease, the cause is unknown.

There are other types of immune hemolytic anemias where the cause may result from an underlying disease or medication. Idiopathic autoimmune hemolytic anemia accounts for one-half of all immune hemolytic anemias. The onset of the disease may be quite rapid and very serious.

Risk factors are not known.