5 min - BioSense Team - 2026-06-24
- level:understanding
- ferritine
- fer
- biomarqueurs
- carence martiale
Ferritin reflects your iron stores, but it is only one of the markers of iron metabolism. This article explains what it actually measures, what a low or high ferritin can mean depending on your profile, and why it is never understood on its own.
Ferritin is one of the most frequently prescribed biomarkers in France. And yet it is also one of the most poorly understood. Is a low ferritin always serious? Does a high ferritin mean "too much iron"? Why does your doctor sometimes order, in parallel, a transferrin saturation or a CRP?
Here is what this marker really tells you about your stores, and how to read it in light of your situation.
What exactly is ferritin?
Ferritin is a protein that stores iron in your cells, mainly in the liver, spleen and bone marrow. The blood ferritin level reflects your iron stores in the body: the higher the ferritin, the larger your stores; the lower it is, the more depleted your stores.
Important: ferritin measures neither the iron circulating in your blood (called serum iron) nor the amount of iron actually available to produce red blood cells (assessed with transferrin and its saturation). It assesses the stock, not the flow. This is precisely why a complete iron work-up — when it is indicated — includes several parameters in parallel.
Another essential point: ferritin is also a so-called "acute-phase" protein. In cases of inflammation, infection, liver damage or certain chronic diseases, it rises independently of iron stores. This is what sometimes makes its interpretation tricky.
Key point — Ferritin reflects your iron stores, but not circulating iron or its availability. It also rises in cases of inflammation, independently of stores. Hence the importance of reading it in context.
Low ferritin: what it can mean
A low ferritin generally reflects a decrease in iron stores. Depending on the laboratory, the usual lower limit is around 15 to 20 µg/L for adult women and 20 to 30 µg/L for men. Below that, we speak of iron deficiency.
An important caveat, already raised in our articles on reference ranges: these thresholds are not universal. Several learned societies, notably the British Society of Gastroenterology, recommend using a higher ferritin threshold, around 30 to 50 µg/L, to rule out functional iron deficiency in the presence of symptoms. In other words, a ferritin of 25 µg/L may be displayed as "normal" on the report and yet explain genuine fatigue.
The most common causes of low ferritin
* Losses: heavy periods, chronic digestive bleeding (sometimes silent), repeated blood donations, endurance athletes (digestive microbleeding and exercise-induced haemolysis). * Insufficient intake: restrictive diet, iron-poor diet (particularly in poorly supervised vegetarians or vegans), malabsorption (coeliac disease, chronic gastritis). * Increased needs: pregnancy, breastfeeding, growth in adolescents.
Possible symptoms
Persistent fatigue, breathlessness on exertion, paleness, hair loss, brittle nails, restless legs sensation, concentration problems. These symptoms can appear well before anaemia sets in — this is known as functional iron deficiency. This is precisely why an iron deficit deserves to be taken seriously even without overt anaemia.
Iron deficiency and iron-deficiency anaemia: not the same thing
Iron deficiency (low iron stores, low ferritin) precedes iron-deficiency anaemia (low haemoglobin due to lack of iron). Not everyone with iron deficiency is anaemic. For many patients it is the reverse: unexplained fatigue is discovered, ferritin is measured, and the deficiency is managed before it becomes anaemia.
Key point — A low ferritin signals a decrease in iron stores. Depending on your context (symptoms, profile, lifestyle), a ferritin between 20 and 50 µg/L may be insufficient even if it is displayed as "normal." The conversation with your doctor starts there.
High ferritin: doesn't necessarily mean "too much iron"
This is the great nuance of this marker, and the main source of confusion. A high ferritin points to two clinically very different situations.
First situation: genuine iron overload
The best-known cause is haemochromatosis, a genetic disease that causes excessive iron absorption. It then translates into a high ferritin associated with a high transferrin saturation (typically above 45-50%). More rarely, overload can be secondary to repeated transfusions or to certain blood disorders. In these cases, the excess iron can accumulate in the organs and requires specialist management.
Second situation, far more common: a high ferritin without overload
In the vast majority of cases, a moderately high ferritin is not due to an excess of iron, but to the rise of ferritin as an acute-phase protein. Several common situations can be responsible:
* Low-grade chronic inflammation (slightly elevated CRP). * Non-alcoholic fatty liver disease — "fatty liver" — often associated with metabolic syndrome (excess weight, prediabetes, high blood pressure). * Excessive alcohol consumption, which often raises ferritin and GGT in parallel. * A chronic inflammatory syndrome (autoimmune diseases, persistent infections).
This is precisely why a high ferritin must always be read alongside CRP, transaminases (ALT, AST), GGT, and ideally transferrin saturation. A high ferritin on its own, without context, cannot be acted upon.
Key point — A high ferritin reflects inflammation, fatty liver or alcohol consumption far more often than genuine iron overload. Transferrin saturation and CRP are essential to sort it out.
Why ferritin is never understood on its own
You've seen it throughout this article: ferritin is a valuable but ambiguous marker. An identical ferritin can mean radically different things depending on your profile and on the other results of the panel.
Three principles for interpreting it usefully:
* A low ferritin in the presence of symptoms (fatigue, breathlessness, hair loss) deserves a discussion even if it sits within the laboratory's "low normal" range. * A high ferritin is never interpreted without CRP, transaminases and transferrin saturation. Without these markers in parallel, you risk a misreading. * Your personal context (age, sex, history, treatments, lifestyle, reason for the prescription) changes the interpretation. That is the whole point of a contextualised reading.
The BioSense method
Ferritin is an excellent example of a biomarker where contextual reading changes everything. BioSense systematically cross-references this result with your health questionnaire (age, sex, menstrual cycles, lifestyle, treatments, reason for the prescription, any symptoms), with the other markers of the iron and inflammation work-up when available, and with official guidelines (HAS, French and international learned societies). Your results are also tracked over time.
*ChatGPT answers you. BioSense knows you.* *BioSense, your prevention companion.* BioSense does not provide a diagnosis and does not replace your doctor. It is a prevention companion that helps you understand, ask the right questions and act day to day.
Preparing for your medical appointment: three useful questions
If your ferritin raises questions — low, high, or simply "borderline" — here are three questions to prepare for your next consultation:
* Given my profile and any symptoms, is my ferritin right for me, or only "within average"? * If it is borderline or abnormal, which additional tests are indicated (transferrin saturation, CRP, transaminases, serum iron)? * What change over time should be monitored, and how often?
This preparation steers the consultation toward a genuine interpretation, rather than a simple observation about the number.
Import your blood test into BioSense and receive a plain-language reading of your ferritin and all your biomarkers, contextualised to your personal profile, compared with official guidelines and tracked over time. Your data is hosted in France on infrastructure certified for hosting health data (HDS).
[→ Import my report](/en/onboarding/upload)
Sources and methodology
* High Authority for Health (HAS) — Choice of iron metabolism tests when iron deficiency is suspected (Appropriate Use fact sheet, 2011): as a first step, measure ferritin alone. * HAS — Assessment of the management of HFE-gene-related haemochromatosis (initial recommendation July 2005, update March 2011). * Snook J, Bhala N, Beales ILP, Cannings D, Kightley C, Logan RP et al. — British Society of Gastroenterology (BSG) Guidelines for the management of iron deficiency anaemia in adults (Gut 2021;70(11):2030-2051, DOI 10.1136/gutjnl-2021-325210). * Académie nationale de Pharmacie, Académie nationale de Médecine and Société Française de Biologie Clinique (SFBC) — Joint session "What reference values in laboratory medicine?" (24 January 2018). * Agence nationale de sécurité sanitaire (Anses) — Update of French nutritional reference values for vitamins and minerals (collective expert report, 2021): iron needs by age and sex. * Santé Publique France — Esteban study 2014-2016, nutrition section (iron status in France).
*BioSense methodology: our content draws on official French guidelines (HAS, ANSM, Santé Publique France, INSERM, Assurance Maladie, Anses), European guidelines (ESC, EASD, NICE) and international ones (WHO, ADA, AHA, NIH), as well as specialised learned societies (SFE, SFBC, GRIO). It is reviewed with an educational approach before publication.*
Going further
* Persistent fatigue after 40: which biomarkers to explore first * Blood test reference ranges: why "within range" isn't enough * Why the same blood result doesn't mean the same thing for everyone
*This article is for informational purposes only and is neither medical advice nor a diagnosis. For any questions about your health, consult your doctor.*