Anemia is a shortage of hemoglobin (HGB). HGB is a protein in red blood cells. It carries oxygen from the lungs to the rest of the body. Anemia causes fatigue, shortness of breath and dizziness. People with anemia don't feel as good as people with a normal level of HGB. They find it harder to work. This is called having a lower quality of life. HGB levels are measured as part of a complete blood count (CBC). See Fact Sheet 121 for more information on these laboratory tests. HGB is measured as grams per deciliter, the amount in a specific sample of blood.

Anemia is defined by the level of HGB. Most health care providers agree that HGB levels below 6.5 indicate life-threatening anemia. Normal levels are at least 12 for women and at least 14 for men. Overall, women have lower levels of HGB. So do very old and very young people. More African-Americans have anemia than people in other ethnic groups.

The bone marrow produces red blood cells. This process requires iron, the vitamins B12 and folic acid (or folate). Erythropoietin (EPO) stimulates the production of red blood cells. EPO is a hormone made by the kidneys.
Anemia can be caused by the body not making enough red blood cells. It is also caused by their loss or destruction. Several factors can cause anemia:
-- Too little iron, vitamin B12 or folate. A shortage of folate can cause megaloblastic anemia, where red blood cells are large and pale.
-- Damage to bone marrow or kidneys.
-- Blood loss from internal bleeding or a woman's menstrual cycle.
-- Destruction of red blood cells (Hemolytic Anemia).