Hemoglobin is the oxygen-carrying protein found within red blood cells. The hemoglobin binds with the oxygen when red blood cells pass through the lungs. The hemoglobin test result is thus used to evaluate how well the red blood cells are able to transport oxygen around the body.
If hemoglobin is low, consider adrenal glands, liver, spleen and bone marrow.
If hemoglobin is high, consider acidosis resulting in lower levels of oxygen (which the body may attempt to counter by increasing number of red blood cells – and thus hemoglobin – to compensate).