Anemia

Anemia is a shortage of red blood cells or of hemoglobin, the iron-containing protein inside them that carries oxygen. Because the blood can carry less oxygen, people with anemia often feel tired and weak, get short of breath on exertion, and may be pale or dizzy. It is a sign of an underlying problem rather than a single disease.

Anemia has three broad causes. Blood loss, for example from heavy menstrual periods or bleeding in the gut, removes red cells faster than they can be replaced. Poor production happens when the bone marrow lacks raw materials such as iron, vitamin B12 or folate, when the marrow itself fails (aplastic anemia), or when diseased kidneys make too little erythropoietin, the hormone that drives red cell production. Excess destruction, called hemolysis, removes red cells early, as in sickle cell disease. Inherited disorders such as thalassemia disrupt hemoglobin and red cell development.

Iron-deficiency anemia is the most common form worldwide, and young children, menstruating girls and women, and pregnant women are the most affected. Infections such as malaria and hookworm add to the burden in many countries. In the lab, anemia is picked up by measuring hemoglobin and red cell counts in a blood sample.