Ferritin is the protein that stores iron inside cells, and the small amount circulating in blood tracks the size of the body's iron reserves. It reflects how much iron is banked in the liver, spleen and bone marrow, and it falls before red-cell counts change. It is also an acute-phase protein, so it answers to inflammation as well as to iron.
No readings for this marker yet.
Low ferritin most often points at depleted iron stores — blood loss, poor absorption, or intake that has not kept up with demand; it is the most specific single marker of iron deficiency. Raised ferritin most often reflects inflammation, infection, liver disease or alcohol rather than iron overload, though inherited iron-loading conditions and repeated transfusions also raise it. Because inflammation lifts it, an unremarkable value does not rule out low stores. One out-of-range result is a reason to re-test and talk to a doctor, not a diagnosis.
Ferritin climbs during any acute illness and for weeks afterwards, so it reads high while an infection or flare is running; iron supplements and recent transfusion lift it too. It is read together with serum iron, total iron binding capacity, transferrin and transferrin saturation, which separate depleted stores from an inflammatory rise. On long-term aspirin, a proton pump inhibitor or oral iron it is usually followed over time rather than judged from a single draw.
Reference ranges are general adult values and depend on lab, assay, age and sex. For orientation, not diagnosis — discuss results with your doctor.