What makes a case of anaemia 'iron deficiency' anaemia?

You are low on iron: Iron is a very important mineral the body uses to make new red blood cells. If you are anemic, it means you are short of red blood cells. You either lost them due to bleeding, you are destroying them too fast (like sickle cell), or you can't make new ones fast enough to keep up with your needs. Whatever the reason, you need the iron (ferrous) to make new ones.