What does ferritin measure?
Ferritin is the body's primary iron storage protein. Low ferritin signals iron depletion — even before hemoglobin falls — and is implicated in fatigue, hair loss, and restless sleep. Ferritin is also an acute-phase reactant and can rise with inflammation.
Full answer
Ferritin reflects total body iron stores and is the most sensitive routinely available marker of iron status. Ferritin falls before hemoglobin in iron deficiency, which is why a 'normal' CBC does not rule out functional iron depletion. Low ferritin is associated with fatigue, exercise intolerance, hair shedding, restless sleep, and — in menstruating women — recurrent depletion. Interpretation requires context: ferritin is an acute-phase reactant, so inflammation, recent illness, or metabolic dysfunction can elevate it independently of iron status. Provider review reads ferritin alongside iron, TIBC, transferrin saturation, hs-CRP, and clinical context before recommending repletion. Self-supplementing iron without that read is not advised.
Educational. Not a substitute for individualized provider review.
- Ferritin — Primary source · oMeds
- Reviewed by Dr. Laura Purdy, MD, MBA · Clinical Director, oMeds · Last reviewed 2026-05-29