Supplementary Material for: The role of hepcidin and an oral iron absorption test in identifying the root cause of iron-restricted anemia

Introduction: Traditional iron parameters often fail to distinguish the cause of iron-restricted anemia in patients without an obvious underlying cause. We evaluated whether an oral iron absorption test (OIAT) and hepcidin measurement could be useful diagnostic tests in these patients. Methods: We retrospectively analyzed data extracted from medical records of all patients who underwent an OIAT and hepcidin measurement, noting subsequent clinical diagnosis. Δ iron >15 µmol/L during the OIAT and hepcidin level below the median (or suppressed ≤0.5 nM) were considered appropriate. Results: Thirty-nine adult patients were included in the study. Sixteen patients with adequate OIAT had suppressed hepcidin levels indicative of classical iron-deficiency anemia (IDA); 59% of patients had abnormal OIAT. In this group, most patients with low hepcidin levels had anemia associated with abnormalities in the gastrointestinal tract, whereas 83.3% patients with high hepcidin levels had iron-refractory iron deficiency anemia (IRIDA), confirmed by genetic testing. Finally, transferrin/log ferritin ratio accurately identified patients with suppressed hepcidin: AUC 0.98 [95% CI: 0.95–1.02], P < 0.001. Conclusion: OIAT differentiates between classical IDA and other types of anemia caused by abnormalities in iron absorption or systemic iron availability. Additionally, elevated hepcidin in patients with oral iron malabsorption could indicate IRIDA.