Ferritin is a multimeric protein made of heavy and light subunits that binds and sequesters iron in a non-reactive form within cells. Biochemically, it functions to buffer free iron, limiting oxidative reactions, and to provide a readily available iron pool for cellular processes. Serum ferritin measured in blood primarily reflects the amount of stored iron in tissues, although it originates from intracellular ferritin released into circulation. Clinically, ferritin has been used for decades as a practical laboratory indicator of iron status. The assay is typically performed by immunoassay and reference ranges vary by age, sex, and laboratory method. Importantly, ferritin also behaves as an acute-phase protein—levels can change with inflammation, liver stress, or metabolic shifts—so interpretation usually relies on additional tests such as CBC, transferrin saturation, and inflammatory markers.

Elevated ferritin levels may reflect larger iron stores but can also rise with inflammation, infection, liver stress, metabolic conditions, or cellular release of iron. Because ferritin is an acute‑phase protein, higher values do not always mean excess body iron and require correlation with markers like C-reactive protein, transferrin saturation, and liver tests. Low ferritin levels most commonly indicate reduced iron reserves and limited iron availability for processes such as red blood cell production and cellular metabolism. Low values should be interpreted alongside hemoglobin, red blood cell indices, and dietary or absorption history to clarify patterns and potential contributors.

Ferritin is included in the Foundation Zoomer as a core Blood Health marker to evaluate iron reserve status and its interaction with inflammatory activity. Within the panel, ferritin helps distinguish patterns of iron availability versus inflammatory-driven elevation and contributes to a clearer, systems-level picture for personalized follow-up and monitoring.