Anemia is a blood disorder that is defined as having fewer red blood cells than normal, or having less hemoglobin than normal.  Hemoglobin is the part of the red blood cells that carry oxygen.

When there are not enough red blood cells or there is too little hemoglobin, the blood is not able to carry enough oxygen to all parts of the body.

There are several different kinds of anemia, such as iron-deficiency, hemolytic, vitamin B12 deficiency, folic acid deficiency, sickle cell, and thalassemia.