What does a low iron saturation level in the blood mean?

Room for iron! Most of the body's iron is bound to that red stuff in our red blood cells, hemoglobin. The rest is bound to proteins, like the blood protein transferrin. If there are still more possible binding sites for iron on transferrin, then the iron saturation is low. This can mean that the body's storage iron is running low. It can be seen before full iron deficiency anemia develops.