Anemia is usually defined as a decrease in amount of red blood cells (RBCs) or the amount of hemoglobin in the blood. It can also be defined as a lowered ability of the blood to carry oxygen.
There are three main types of anemia, that due to blood loss, that due to decreased red blood cell production, and that due to increased red blood cell breakdown.
Anemia is the most common disorder of the blood with it affecting about a quarter of people globally. Iron-deficiency anemia affects nearly 1 billion. It is more common in females than males among children, during pregnancy and in the elderly.