What is red cell zinc protoporphyrin (ZPP)?

By William Aird

A trace byproduct of the last step in heme synthesis. In iron deficiency, zinc, instead of iron, is incorporated into the protoporphyrin ring, resulting in increased zinc protoporphyrin levels (iron protoporphyrin is also called heme). ZPP may be used as an assay for iron deficiency.

Heme synthesis from succinyl-CoA to PPIX and ultimately heme. Synthesis of ALA is the rate-limiting step and under negative feedback control of heme (green/ dashed). A deficiency of iron supply limits heme synthesis and leads to PPIX accumulation. Zinc can then substitute for iron and ferrochelatase catalyzes the formation of zinc PPIX (red/dotted). From the following link.