Anemia Definition and Symptoms

Red blood cells
Red blood cells seen under the microscope. Photo © A.D.A.M.


Blood contains red cells, white cells, and platelets. The red blood cells (RBCs) carry oxygen throughout the body. Men have about 5.2 million red blood cells per cubic millimeter of blood, and women have about 4.7 million per cubic millimeter of blood. (A cubic milliliter is about the same amount of liquid as a tiny blood spot.)

Anemia means an abnormally low number of red cells in the blood.

Anemia can be caused by:

  • inherited genetic conditions
  • chronic disease such as kidney disease or certain cancers
  • medications such as ribavirin, Dilantin (phenytoin), or methotrexate
  • Vitamin B deficiency
  • iron deficiency
  • losing a lot of blood
  • too many red blood cells being destroyed by the body (called hemolytic anemia)
  • not enough red cells being produced by the body in conditions such as aplastic anemia or thalassemia
  • chemotherapy or radiation therapy
Because there are low numbers of red blood cells, not enough oxygen reaches the body's tissues. Symptoms of anemia include:
  • weakness and fatigue
  • pale skin
  • shortness of breath with physical activity
  • lightheadedness or dizziness
  • rapid heartbeat
  • headache
Anemia is diagnosed by a blood test called a complete blood count (CBC). A blood sample is taken and its amount of red blood cells are measured.


"Anemia." Health Topics A-Z. 01 Jan 2008. A.D.A.M.. 9 Mar 2009.

Pronunciation: a-NEE-me-a

Alternate Spellings: anaemia

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