In cases of iron deficiency the RBCs produced by the bone marrow are too small and therefore low in their oxygen-carrying capacity. Normally this condition is caused by some kind of blood loss. Although blood loss can happen anywhere, the most common site of the blood loss is the gastrointestinal tract since mostly it can go undetected. Some symptoms include decreased growth rate, anorexia, weakness, lethargy, depression, rapid breathing, increased susceptibility to disease, and tarry stools.
