Table 1.

Free iron forms types and property.

Acronym	Meaning	Characteristic	Chemical composition	Redox active	Ability to enter cell by a transferrin independent way	Chetable
NTBI	non-transferrin bound iron	Circulating iron not bound to transferrin, ferritin or heme.	Heterogeneous. Several circulating isoforms that is FE(III) bound to albumin, citrate and potentially to acetate, malate and phosphate.	No	Yes	Yes
LPI	labile plasma iron	Fraction of NTBI that is redox active, potentially toxic. Also defined as extracellular counterpart of LCI	Heterogeneous. Components are the same of NTBI,	Yes	Yes	Yes
LCI	labile cellular iron	Fraction of the cellular iron pool that promotes ROS formation when it raises to “relatively high” levels*	It is comprised of complexes of iron with nucleotides, gluthathione and carboxylates	Yes	Na	Yes
eLPI	enhanced labile plasma iron**	Fluorescence-based assay indicative of total NTBI. See above

^*defined as levels that surpass cell innate capacity to produce sufficient ferritin or antioxidant that counteract formation of ROS

^**See Methods on Reference n° 17: Wermke M et al, Lancet Haematol 2018.