TransferrinSiderophilin
The protein that carries iron around the blood.
Transferrin is the liver-made protein that binds iron and transports it to the bone marrow and other tissues. Free iron is chemically reactive, so the body keeps almost all of it bound in transit.
It matters because the body adjusts how much it makes according to need: production typically rises when iron is short, as the system tries to capture more of what is available, and falls with inflammation and liver disease.
In practice transferrin is read with iron and ferritin, and its capacity to carry iron is often reported instead as total iron binding capacity, which measures the same property from the other direction.