Anemia occurs when there are not enough healthy red blood cells to carry oxygen to the body's organs. The most common type is iron-deficiency anemia, which can be caused by blood loss or not getting enough iron in the diet. Anemia is diagnosed through a blood test called a complete blood count. Treatment depends on the underlying cause but may include iron supplements, changing diet, or blood transfusions. Maintaining a healthy diet with iron and vitamins can help prevent some forms of anemia.