Does inflammation increase hepcidin and alter iron trafficking while low ferritin argues against inflammation as the main cause?

Systemic iron homeostasis is tightly controlled by the liver-derived hormone hepcidin, which is highly responsive to inflammatory signaling. However, distinguishing between inflammatory iron sequestration and absolute iron depletion is critical for appropriate clinical management.

Mechanistic explanations

• The IL-6/JAK/STAT3 pathway: During inflammation, immune and stromal cells release interleukin-6 (IL-6). IL-6 binds to its receptor complex on hepatocytes, activating Janus kinases (JAKs) and phosphorylating STAT3. Phosphorylated STAT3 translocates to the nucleus, binding to the HAMP promoter to strongly upregulate hepcidin transcription.
• Ferroportin degradation: Hepcidin acts as a ligand for ferroportin, the sole cellular iron exporter located on duodenal enterocytes, macrophages, and hepatocytes. Hepcidin binding induces the internalization and lysosomal degradation of ferroportin.
• Iron sequestration: The loss of ferroportin halts cellular iron export. This blocks dietary iron absorption in the gut and traps recycled iron inside macrophages and hepatocytes, leading to systemic hypoferremia and restricted erythropoiesis.

Clinical evidence and ferritin dynamics

• Ferritin as an acute-phase reactant: Ferritin synthesis is upregulated by pro-inflammatory cytokines. Consequently, pure inflammatory iron sequestration (anemia of chronic disease) is characterized by normal or elevated serum ferritin levels.
• Significance of low ferritin: A low serum ferritin level is highly specific for absolute iron deficiency (depleted physical stores). While inflammation artificially inflates ferritin levels, a strictly low ferritin value—typically $<30$ ng/mL, or $<100$ ng/mL in patients with active inflammatory disease—demonstrates that total body iron stores are exhausted.
• Implications for etiology: When ferritin is low, the primary driver of restricted iron availability is an absolute lack of elemental iron rather than inflammation-induced retention of adequate stores.

Bottom line

While inflammation elevates hepcidin to sequester iron via ferroportin degradation, a low ferritin level ($<30$ ng/mL, or $<100$ ng/mL during active inflammation) confirms absolute iron depletion, ruling out inflammation as the primary or dominant cause of the iron-restricted state.