I read that during a blood test your doctor checks as to whether you have a normal amount of healthy red cells. A shortage spells anemia. If that exists, it might mean that you need more iron-containing food in your diet. But a low red-cell count also alerts your doctor to check to see if you might be losing blood internally, as from a bleeding ulcer. Or a serious deficiency could be caused by some problem in your bone marrow. In any event, the condition should be investigated carefully, for there is no known substitute for red cells in bringing oxygen to your body cells.