Ferritin levels show how much iron the body has in reserve, mostly stored in the liver, spleen and bone marrow. A blood test ordered by a general practitioner, usually drawn after fasting, is used to spot an iron deficiency or, conversely, an iron overload. Read on its own, the result stays ambiguous: it also rises with inflammation, regardless of actual iron status.
In brief – Ferritin is the protein that stores iron in the body, and blood ferritin levels indicate how much iron is held in reserve. A low result (below 15 to 30 micrograms per liter, depending on age) most often signals iron deficiency, with a risk of fatigue and anemia over time. A high result (above 200 to 300 micrograms per liter) can reflect iron overload, but just as often simple inflammation, liver disease or regular alcohol use, since this protein also rises during the acute phase of inflammation. The result should always be read alongside serum iron, transferrin (or its saturation percentage) and, if needed, CRP. A single number, without these companion markers or clinical context, does not allow a firm conclusion.
Definition: What Do Ferritin Levels Measure?
Ferritin is a storage protein that keeps iron in a non-toxic form inside cells. About 70% of the body’s iron circulates in the hemoglobin of red blood cells; the rest forms a reserve, mainly in the liver, spleen and bone marrow, of which ferritin is the indirect blood marker. Results are reported in micrograms per liter (µg/L), the same numeric value as nanograms per milliliter (ng/mL), the unit many US lab reports use.
A serum ferritin test therefore does not measure the iron circulating in the blood at a given moment, that is the role of serum iron and transferrin, but the state of accumulated reserves. This is why it is the first-line test recommended to screen for iron deficiency, even before anemia becomes detectable on a complete blood count.
Mechanism: Why Do Ferritin Levels Change?
Ferritin depends on two separate mechanisms, which is why the result is never read in isolation. On one hand, it mirrors the balance between dietary iron intake, intestinal absorption and losses (menstruation, blood donation, digestive bleeding). On the other, ferritin is also an acute-phase protein: the liver makes more of it in response to infection, chronic disease or excess body fat, independent of actual iron status.
- Heme iron (meat, fish, offal): intestinal absorption of about 15%, notably higher than non-heme iron.
- Non-heme iron (legumes, grains, leafy greens): absorption of about 5%, improved by vitamin C and reduced by tea, coffee or calcium taken at the same meal.
- Hepcidin: a liver hormone that blocks intestinal iron absorption and its release from macrophages once reserves are sufficient or during inflammation.
- Acute or chronic inflammation: can push the result up temporarily, masking an underlying iron deficiency.
What the Science Says About Ferritin Levels and Blood Thresholds
The threshold for iron deficiency varies by age and by the population studied. Among 1,254 people aged 60 to 95 followed as outpatients, a serum level of 22 micrograms per liter was identified as the cutoff for iron deficiency, with 89.5% sensitivity and 89% specificity (Choi et al., 2005). This threshold, lower than the one used in hospitalized adults, shows why laboratory reference ranges must always be read alongside clinical context.
The link with mortality is not the same for men and women. In an English cohort of 5,471 adults aged 52 and older followed for an average of 7.7 years, a high result was associated with higher cardiovascular and all-cause mortality in men without major chronic disease (adjusted relative risk of 1.49), while in women it was the lowest results that were linked to higher all-cause mortality (Kadoglou et al., 2017). These findings show an association, not a proven direct cause.
In chronic inflammatory disease (inflammatory bowel disease, heart failure, chronic kidney disease), ferritin loses some of its reliability because inflammation raises it regardless of iron status. In these cases, the authors recommend a threshold below 100 micrograms per liter, or a transferrin saturation below 20%, to identify iron deficiency despite an apparently normal result (Dignass et al., 2018). According to nutrient fact sheets from the NIH Office of Dietary Supplements, heme iron remains the best-absorbed dietary source, which explains why diets low in animal foods carry a higher risk of low ferritin levels.
In Practice: How to Interpret Your Ferritin Levels
A result should always be read in light of sex, age and clinical context: pregnancy, heavy periods, intense endurance training, alcohol use or a known inflammatory disease. The table below offers general reference points, to confirm with a healthcare professional.
| Ferritin level | Indicative values | Possible interpretation |
|---|---|---|
| Low | Below 15 to 30 micrograms per liter, depending on age | Likely iron deficiency, risk of iron-deficiency anemia over time |
| Normal (adult) | About 30 to 200 micrograms per liter (women) / 30 to 300 micrograms per liter (men) | Iron reserves considered adequate |
| High | Above 200 to 300 micrograms per liter | Inflammation, liver disease, alcohol use, metabolic syndrome or iron overload to investigate |
| Very high | Above 1,000 micrograms per liter | Urgent workup needed (hemochromatosis, liver disease, severe inflammatory syndrome) |
The people most at risk of a low result are menstruating women with heavy periods, pregnant women, endurance athletes and people following an unsupplemented vegetarian or vegan diet. To place this marker among the other metabolic health indicators tracked over time, our longevity blood marker protocol explains how to cross-reference several biomarkers rather than rely on a single figure. Since this marker also rises with low-grade inflammation, our article on chronic inflammation (inflammaging) explains how it can blur the interpretation of several blood markers, ferritin included. The signaling loop between inflammation and iron regulation is part of the broader biology covered in our pillar on intercellular communication.
Protocol: What to Do Based on Your Result
Faced with a low or high result, the first step is not to self-diagnose or self-supplement, but to confirm it with complementary markers.
- Confirmed low ferritin levels: ask for serum iron and transferrin testing, look for a cause of loss (menstruation, digestive bleeding), then discuss with a doctor whether supplementation is warranted and for how long.
- Isolated high result: recheck CRP to rule out ongoing inflammation before concluding there is iron overload.
- Persistently high result: a transferrin saturation test can point toward genetic testing for hereditary hemochromatosis (HFE gene mutation) if saturation exceeds 45%.
- Diet: pair non-heme iron sources with a vitamin C-rich food, and space out tea or coffee from main meals to improve absorption.
- Follow-up: a recheck at 3 months is usually suggested after correcting a deficiency, to allow reserves to rebuild.
Frequently Asked Questions About Ferritin
What is the difference between ferritin and serum iron?
Ferritin measures the iron reserves stored in tissues, while serum iron measures the iron circulating in the blood at a given moment. Serum iron fluctuates widely throughout the day and with meals, which makes it less reliable on its own. More stable, ferritin remains the reference test for assessing the body’s overall iron reserves.
What are the symptoms of low ferritin?
A low result can stay silent for a long time before anemia appears. The most common signs include persistent fatigue, breathlessness on exertion, pale skin, headaches, hair loss or brittle nails. These symptoms are not specific and need to be confirmed with blood testing before any interpretation.
Is a high ferritin level always serious?
No. A high result most often reflects temporary inflammation, alcohol use, metabolic syndrome or liver disease, well before an actual iron overload. Only a confirmed elevation, combined with a high transferrin saturation, justifies a deeper search for a cause, including hereditary hemochromatosis.
How can you lower ferritin that is too high?
Management depends entirely on the cause identified by a doctor. It can include cutting back on alcohol, losing weight in cases of metabolic syndrome, treating an underlying liver disease or, in confirmed hemochromatosis, regular therapeutic phlebotomy under medical supervision. No self-treatment should be started without an established diagnosis.
How often should ferritin be tested?
There is no universal frequency: testing is warranted when symptoms suggest it, when risk factors are present (heavy periods, a vegetarian diet, repeated blood donation) or as part of follow-up after correcting an abnormal result. Outside of these situations, routine testing without a medical reason is not recommended.
Medical disclaimer. The information provided here is for informational purposes only and does not constitute medical advice. It does not replace a consultation. Ask a healthcare professional before changing your diet, taking dietary supplements or starting a new practice, especially if you have a medical condition, are pregnant or are under treatment. Dietary supplements do not replace a balanced diet or medical follow-up.
