What is the role of ferritin in iron studies and what caveat can make it misleading?

• A. Ferritin reflects iron stores but rises with inflammation as an acute-phase reactant; low ferritin indicates iron deficiency, high ferritin does not exclude iron overload or functional iron deficiency.
• B. Ferritin measures transferrin saturation directly and is unaffected by inflammation.
• C. Ferritin rises only with iron overload and drops during inflammation.
• D. Ferritin is a direct marker of erythropoietin activity and is unrelated to iron stores.

Answer: (A)

Ferritin is the storage form of iron, so serum ferritin generally reflects the body’s iron stores: low ferritin strongly suggests iron deficiency. However, ferritin is also an acute‑phase protein that rises with inflammation, infection, liver disease, and other inflammatory states. This means that ferritin can be elevated even when iron stores are limited, potentially masking iron deficiency. Conversely, ferritin can be high due to inflammation even if iron overload isn’t present, so a high ferritin alone doesn’t confirm ample iron or rule out iron‑restricted conditions.

In practice, interpret ferritin alongside inflammatory markers and other iron indices. If inflammation is present, a normal or elevated ferritin may not rule out iron deficiency, and a low ferritin remains a clear indicator of deficiency. For functional iron deficiency—where iron is sequestered and unavailable for erythropoiesis despite adequate stores—ferritin can be high or normal, while transferrin saturation may be low, illustrating why relying on ferritin alone can be misleading.