Ferritin is the protein that stores iron inside cells, and the blood test named after it is the standard first estimate of how much iron your body holds in reserve. Most of it sits in the liver, spleen and bone marrow, and a small fraction leaks into the blood in proportion to those stores. It is the earliest marker to fall when iron runs short, well before hemoglobin. It is also an acute-phase protein, so infection, inflammation, liver disease and alcohol push it up whether or not there is iron behind the number.
What it measures
Serum ferritin comes from an ordinary venous blood draw, run on an immunoassay, and is reported in ng/mL or in micrograms per liter – the two units are numerically identical, so 20 ng/mL and 20 mcg/L are the same result. It is a stores marker, not a snapshot of circulating iron: serum iron swings with meals and time of day, and transferrin describes the transport protein rather than the reserve. For a deeper reference on the test, see the Ferritin entry at Smart Longevity.
Typical values
| Result | What it generally means |
|---|---|
| Below 15 ng/mL (mcg/L) | Depleted iron stores in adults, by the long-standing WHO threshold, absent inflammation |
| Roughly 15-30 ng/mL | Many hematology guidelines still call this iron deficiency, especially with symptoms |
| Inside your laboratory’s reference interval | Reported as normal; the interval differs by lab and assay and is wider and higher for men |
| Above your laboratory’s upper limit | Needs an explanation – inflammation and liver disease raise it far more often than true iron overload does |
Limits are set by each laboratory, differ by sex and age, and in women typically rise after menopause once menstrual losses stop. Two results are only comparable if they come from the same assay. Because inflammation lifts ferritin, a normal-looking value alongside a raised inflammatory marker does not rule out deficiency, and clinicians commonly read ferritin next to Transferrin saturation (TSAT), which stays low in deficiency and runs high in genuine iron overload.
Why it matters for longevity
Both ends of the range carry meaning. Low ferritin is common in menstruating women, endurance athletes and people with slow gastrointestinal blood loss, and it is associated with fatigue, reduced exercise capacity and restless legs before anemia appears; in an older adult it is a reason to look for a source of bleeding, not just a number to top up. High ferritin is associated in observational cohorts with metabolic syndrome, type 2 diabetes, fatty liver and cardiovascular disease, but most of those associations likely run through inflammation rather than iron, which is why a raised ferritin is read alongside hs-CRP — high-sensitivity C-reactive protein. True iron overload is a different matter: hereditary hemochromatosis loads iron into the liver, heart, pancreas and joints over decades, and the damage it does is preventable if it is found early. Tissue iron tends to accumulate with age, and iron-driven cell death is an active line of aging research, but that link remains a hypothesis.
What changes it
Blood loss is the strongest downward lever: heavy periods, gastrointestinal bleeding and regular donation all draw stores down, and donors often run low ferritin with a normal hemoglobin. Diet moves it slowly. Heme iron from meat and fish absorbs best; vitamin C improves absorption of plant iron, while tea, coffee and calcium taken with the meal reduce it. Oral iron raises ferritin over months rather than weeks, and alternate-day dosing is often absorbed better than daily dosing. Take it only for a documented deficiency – iron does nothing for anemia that is not iron-related, and excess iron is harmful. Upward, ferritin follows inflammation, infection, alcohol, fatty liver and repeated transfusions; treating the underlying condition brings an inflammatory ferritin down. For diagnosed hemochromatosis, scheduled phlebotomy is the standard treatment. Your sex and your genes are not levers you control.
Related reading
- Which Blood Tests Reflect Aging and How to Read Them
- Chronic Inflammation and Aging: Inflammaging
- How to Build a Longevity Supplement Plan
- Hemoglobin
Disclaimer. This article is for information only and does not replace medical advice. Talk to a qualified clinician before changing anything about your health.