Low ferritin what causes it?

Iron deficiency: Ferritin is the 'storage' form or 'warehouse' of iron. If you have been told your ferritin is low, it is probably because either A) you are not eating enough iron in your diet, or B) you have some blood losses (heavy periods). Another choice might be C) disease processes with malnutrition, inadequate absorption, or utilization. You should follow through with your doctor to get this problem fixed.