Ferric Carboxymaltose in Heart Failure with Iron Deficiency

To the Editor: The definition of iron deficiency that has been widely adopted in the care of patients with heart failure and in the HEART-FID trial by Mentz et al. (Sept. 14 issue)(1) blurs the difference between absolute and functional iron deficiency, a distinction that is evident in the bone marrow of patients with heart failure.(2) Functional iron deficiency is characterized by a transferrin saturation (TSAT) of less than 20%, with normal or elevated ferritin levels. In the accompanying editorial, Martens and Mullens(3) discuss why patients with a ferritin level of less than 100 ng per milliliter may be eligible . . .