What is functional iron deficiency?
Functional iron deficiency is a bone marrow iron supply-demand mismatch in a patient with normal or elevated iron stores.
It can occur in the setting of inflammation when elevated hepcidin levels impair the release of storage iron to circulating transferrin.
It can also occur in patients treated with pharmacologic doses of ESAs when the bone marrow is stimulated to produce RBCs faster than the transferrin carrier protein can deliver adequate iron substrate.
In such patients, TSAT tends to be low or low-normal, whereas serum ferritin level may be normal or even high.
The operative definition of functional iron deficiency is based on a response to intravenous (IV) iron supplementation characterized by either an increase in Hb or a decrease in ESA requirements to achieve the same Hb.