Anemia happens when the number of healthy red blood cells in your body is too low. Red blood cells carry oxygen to all of the body’s tissues, so a low red blood cell count indicates that the amount of oxygen in your blood is lower than it should be.

Many of the symptoms of anemia are caused by decreased oxygen delivery to the body’s vital tissues and organs.

Anemia is measured according to the amount of hemoglobin — the protein within red blood cells that carries oxygen from the lungs to the body’s tissues.