Hemolytic anaemia describes the condition in which this loss of red blood cells occurs because the red cells break up (lyse). This can happen inside the blood vessels (intravascular hemolysis) or outside of the blood vessel (extravascular hemolysis). Hemolytic anaemia can occur for many reasons, including heat stroke, parasites, viral infections. toxins and other conditions.

One of the things that can cause hemolytic anaemia is immune system disease --- in this case the disorder is known as immune mediated hemolytic anaemia (IMHA). This is the term currently preferred for the condition formerly known as auto-immune hemolytic anaemia (AIHA). The reason for the subtle name change is the recognition that much of the time the immune system really is attacking an invader -- it just happens to be one that is stuck on the red blood cell so both get destroyed.