TFRC and hemoglobinopathy: In addition, more than half of the participants (55%) had serum transferrin receptor concentrations >8.5 mg/L, and 81% showed high zinc protoporphyrin values (>40 mmol/mol heme).10 On the other hand, ID based on serum transferrin receptor levels may have been overestimated, as the study was not able to exclude hemoglobinopathies.11 Likewise, zinc protoporphyrin may have been elevated by increased erythropoiesis caused by hemoglobinopathies and/or inflammation.12 We can cautiously assume that 27% of anemic girls had iron as an underlying cause.