Iron and ferritin are not the same thing. Iron is the mineral the body uses for oxygen transport, energy production, and many biologic processes. Ferritin is the protein that stores iron. In other words, iron is the resource itself, while ferritin reflects how that resource is stored. This distinction is clinically important because serum iron can appear normal while ferritin is low, meaning that circulating iron is acceptable but reserve stores are being depleted. Likewise, ferritin can be high while serum iron is normal or even low in certain situations. To interpret iron-related lab results correctly, this difference must be clearly understood. That is why iron deficiency assessment relies not only on serum iron, but also on ferritin and related markers.