TFRC and autosomal erythropoietic protoporphyria: However, serum iron concentrations and soluble transferrin receptor-1 (sTfR), a marker of iron deficiency and ineffective erythropoiesis, have been reported to be normal, confirming the iron is sufficient for hemoglobin synthesis in EPP (Holme et al., 2007; Delaby et al., 2009).