Anemia refers to any condition in which the number of red blood cells (RBCs) in the body or the amount of the oxygen-carrying molecule that red blood cells contain — called hemoglobin — is too low. In either case, the result is a reduced capacity of the blood to carry oxygen, which causes fatigue, weakness, and sometimes other problems.

Anemia can have several causes including blood loss, nutrient deficiency, and genetic mutations. Depending on the cause, symptoms can be temporary or long-lasting and range from mild to severe. The treatment for anemia depends on the cause and may be as simple as taking a vitamin or it may require transfusions and/or more invasive treatments.

Anemia is a relatively common disorder and among certain populations it is even more common. For example, researchers estimate that 10% of people over 65 and 15-20% of women aged 12-49 have anemia. Additionally, 30% of people with HIV, 50% of critically ill patients in intensive care units, and 80% of chemotherapy patients have some type of anemia.