Causes

Stem cells in the bone marrow produce blood cells — red cells, white cells and platelets. In aplastic anemia, stem cells are damaged. As a result, the bone marrow is either empty (aplastic) or contains few blood cells (hypoplastic).

The most common cause of aplastic anemia is from your immune system attacking the stem cells in your bone marrow. Other factors that can injure bone marrow and affect blood cell production include:

• Radiation and chemotherapy treatments. While these cancer-fighting therapies kill cancer cells, they can also damage healthy cells, including stem cells in bone marrow. Aplastic anemia can be a temporary side effect of these treatments.
• Exposure to toxic chemicals. Toxic chemicals, such as some used in pesticides and insecticides, and benzene, an ingredient in gasoline, have been linked to aplastic anemia. This type of anemia might improve if you avoid repeated exposure to the chemicals that caused your illness.
• Use of certain drugs. Some medications, such as those used to treat rheumatoid arthritis and some antibiotics, can cause aplastic anemia.
• Autoimmune disorders. An autoimmune disorder, in which your immune system attacks healthy cells, might involve stem cells in your bone marrow.
• A viral infection. Viral infections that affect bone marrow can play a role in the development of aplastic anemia. Viruses that have been linked to aplastic anemia include hepatitis, Epstein-Barr, cytomegalovirus, parvovirus B19 and HIV.
• Pregnancy. Your immune system might attack your bone marrow during pregnancy.
• Unknown factors. In many cases, doctors aren't able to identify the cause of aplastic anemia (idiopathic aplastic anemia).

Connections with other rare disorders

Some people with aplastic anemia also have a rare disorder known as paroxysmal nocturnal hemoglobinuria, which causes red blood cells to break down too soon. This condition can lead to aplastic anemia, or aplastic anemia can evolve into paroxysmal nocturnal hemoglobinuria.

Fanconi's anemia is a rare, inherited disease that leads to aplastic anemia. Children born with it tend to be smaller than average and have birth defects, such as underdeveloped limbs. The disease is diagnosed with the help of blood tests.