Figure 1.

Red blood cell (RBC) zinc protoporphyrin progressively increases with increasing severity of iron deficiency.

Iron deficiency progresses from reduced iron stores to iron depletion, in which there is normal erythropoiesis with normal zinc protoporphyrin levels, but decreased ferritin due to absent iron stores. The next stage is iron-deficient erythropoiesis, in which increased RBC levels of zinc protoporphyrin and very low serum ferritin levels reflect both absent iron stores and the lack of sufficient iron for normal haemoglobin production. As iron deficiency progresses further, frank iron deficiency anaemia develops with insufficient iron for maintaining adequate haemoglobin levels. Adapted from Hastka J et al. and Brittenham GM¹,².