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Section 2 of 6 · Open sections

Required section · Section 2 of 6

Basic mental model: traffic control and storage

Iron enters plasma from intestinal enterocytes and from macrophage and hepatocyte stores. Transferrin carries circulating iron, while ferritin is the principal intracellular storage protein. Transferrin saturation is the percentage of iron-binding capacity occupied by iron.

Hepcidin binds ferroportin on enterocytes, macrophages, and hepatocytes, promoting ferroportin internalization and degradation. Low hepcidin permits more absorption and release from stores. Hepcidin-mediated retention lowers plasma iron in inflammatory states, while ferritin can increase as an acute-phase reactant. This separates an acute-phase storage signal from increased circulating iron availability.

When iron remains available beyond transport and storage needs, deposition in organs is a clinical concern, not a result directly produced by the iron panel. This model is reusable because it separates transport, storage, and tissue burden before a pattern is named. Calculate saturation from the released iron and TIBC values, then interpret it beside ferritin rather than in isolation.

Illustrative drawing — this picture was drawn rather than captured.

Diagram showing iron moving from an intestinal absorption compartment through ferroportin into transferrin-containing plasma and to liver ferritin storage, with hepcidin limiting ferroportin-mediated plasma entry.
Figure 1Iron movement between the intestinal absorption compartment, plasma, liver storage, and hepcidin-regulated ferroportin.

Use the compartment model before deciding what a high ferritin means.

  1. Identify the measurement

    Separate serum iron, TIBC, ferritin, and calculated saturation.

  2. Locate the signal

    Decide whether the signal is transport, storage, or a possible tissue-burden question.

  3. Check hepcidin context

    Consider inflammation and liver context that can change circulating iron or ferritin.

  4. Bound the conclusion

    State what supports a workup and what still requires clinical correlation.

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Knowledge check 1

What is the direct effect of hepcidin binding to ferroportin?

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