What is ferritin?
Ferritin is an iron-storage protein found in the body's cells, primarily in the liver, spleen, and bone marrow. The protein's main function is to store iron in a safe, bioavailable form so that the body can use it when needed. Iron is an essential mineral required for, among other things, the production of Hemoglobin—the oxygen-transporting protein in red blood cells. Iron is also a component of several enzymes vital for cellular energy metabolism and normal function.
A small amount of ferritin circulates in the blood. The concentration of ferritin in serum or plasma—often referred to as S-ferritin or P-ferritin—serves as an indirect marker of the body's iron stores. In individuals without concurrent inflammation, there is a clear correlation between ferritin concentration and the amount of stored iron. Ferritin is one of the most important laboratory markers when investigating iron deficiency. A low ferritin level can indicate that the body's iron stores are depleted or reduced, even before hemoglobin levels drop and anemia develops.
At the same time, ferritin is an acute-phase protein, meaning its concentration can rise during inflammation, infection, and certain medical conditions.
Therefore, the ferritin level must always be assessed in conjunction with other blood test results, symptoms, and medical circumstances.Ferritin – reference values and interpretation
Ferritin is typically measured in micrograms per liter (µg/L). Reference ranges vary between laboratories and are influenced by factors such as age, sex, the analytical method used, and physiological conditions. It is important to distinguish between the laboratory’s reference range—which describes the distribution of values in a reference population—and medical decision limits used to assess the likelihood of iron deficiency.
The following levels are often used as a guide for the clinical assessment of adults:
| Ferritin level | Medical interpretation |
|---|---|
| Below 15 µg/L | Strongly suggests depleted iron stores in otherwise healthy adults. |
| 15–29 µg/L | Usually suggests low iron stores and may indicate iron deficiency. |
| 30–45 µg/L | Iron deficiency may still be present, especially in the presence of symptoms, anemia, or other supporting findings. |
| 46–100 µg/L | Requires interpretation based on the clinical situation. Iron deficiency can occur in the presence of concurrent inflammation. |
| Above 100 µg/L | Usually argues against pronounced absolute iron deficiency in the absence of inflammation, but does not rule out functional iron deficiency. |
These levels serve as a guide and do not constitute a universal reference range. In cases of infection or inflammation, ferritin levels may be elevated despite a lack of available iron. A ferritin level below 70 µg/L in adults with inflammation can indicate iron deficiency, but this threshold should never be used as a general diagnostic cutoff for all patients.
Specific assessment criteria apply to pregnant women and children.
What is a normal ferritin level for women and men?
Ferritin levels are often lower in menstruating individuals, as regular blood loss increases the body's iron requirements. After menopause, ferritin levels often rise, approaching the levels seen in men. Men generally have larger iron stores than menstruating women, though there is significant individual variation.
Consequently, there is no single optimal ferritin level that applies to everyone. A value within the laboratory's reference range does not necessarily rule out iron deficiency, nor does an elevated value necessarily indicate iron overload. When interpreting test results, the laboratory's current reference range should be used in conjunction with relevant medical decision limits.
What does low ferritin mean?
Low ferritin indicates depleted iron stores. It is often an early laboratory finding in iron deficiency and may appear before hemoglobin concentration is affected. Iron deficiency usually develops gradually. Initially, the body uses its stored iron to maintain normal functions. As these stores are depleted, ferritin levels drop. If the iron deficiency persists, the iron supply available for red blood cell production may become insufficient, which can eventually lead to iron-deficiency anemia.
Common causes of low ferritin
- Blood loss: Heavy menstrual periods, gastrointestinal bleeding, or frequent blood donations can deplete iron stores.
- Insufficient iron intake: Low dietary iron intake can contribute to iron deficiency, especially when iron requirements are elevated.
- Increased iron requirements: The body's need for iron increases during pregnancy, periods of growth, and other specific physiological stages.
- Impaired iron absorption: Celiac disease, certain gastrointestinal disorders, and previous gastrointestinal surgeries can hinder iron absorption.
- Combination of factors: Iron deficiency can result from a combination of blood loss, increased requirements, and insufficient intake.
In adult men and individuals who do not menstruate, confirmed iron deficiency often requires investigation, with particular attention paid to potential sources of gastrointestinal bleeding.
Can you have low ferritin without anemia?
Yes. Iron deficiency without anemia means that the body's iron stores are depleted, while hemoglobin levels remain within the reference range.
This can occur during the early stages of iron deficiency. Some individuals experience fatigue or reduced physical endurance, while others show no clear symptoms.
Therefore, a normal hemoglobin level does not rule out iron deficiency.
If iron deficiency is suspected, ferritin levels can provide important information even when the complete blood count is normal.Symptoms of iron deficiency and low ferritin
Iron deficiency can cause varying symptoms depending on the severity of the deficiency, its duration, and whether anemia has developed.
Common symptoms of iron deficiency or iron-deficiency anemia include:
- Fatigue and reduced energy levels.
- Impaired physical performance.
- Difficulty concentrating.
- Headache and dizziness.
- Shortness of breath upon exertion, especially if anemia is also present.
- Heart palpitations, particularly in cases of more severe anemia.
- Restless legs (Restless Legs Syndrome).
- In some cases, hair loss or changes to the nails and mucous membranes.
These symptoms are non-specific and can occur with many other conditions. A ferritin test can therefore aid in the diagnostic process but cannot, on its own, explain the cause of symptoms such as fatigue, dizziness, or hair loss.
What does high ferritin mean?
An elevated ferritin level means that the concentration of ferritin in the blood is higher than the laboratory's reference range. However, this does not necessarily mean that the body has excessive iron stores.
Ferritin also functions as an acute-phase protein and can rise as part of the body's inflammatory response. Elevated levels can therefore occur in various conditions unrelated to iron overload.
Common causes of elevated ferritin
- Inflammation and infection: Inflammatory processes can increase ferritin concentration independently of the body's iron stores.
- Liver disease: Ferritin levels can rise in conditions such as fatty liver, liver inflammation, and alcohol-related liver damage.
- Metabolic conditions: Excess weight, insulin resistance, and metabolic syndrome can be associated with elevated ferritin levels.
- Iron overload: Hereditary hemochromatosis and certain other conditions can lead to increased iron accumulation.
- Other medical conditions: Certain chronic inflammatory diseases, blood disorders, and cancers can also affect ferritin levels.
When ferritin levels are elevated, transferrin saturation is an important supplementary blood test for assessing whether there are signs of iron overload.
A markedly elevated ferritin level—particularly around or above 1,000 µg/L—should prompt a medical assessment and investigation into the underlying cause.
Even lower, persistent elevations may require investigation, depending on other findings.Ferritin and inflammation – why can the test result be misleading?
Since ferritin is an acute-phase protein, its concentration can rise during inflammation, even if the body's iron stores are simultaneously low. This is particularly relevant in cases of chronic inflammatory diseases, infections, and certain long-term medical conditions.
During inflammation, the body may increase production of the hormone hepcidin, which regulates iron metabolism. Hepcidin reduces iron absorption from the gut and limits the release of stored iron into the bloodstream. The result can be that iron is stored in the body but is not sufficiently available for the production of red blood cells.
This is sometimes referred to as functional iron deficiency and differs from absolute iron deficiency, where the body's iron stores are actually depleted. If inflammation is suspected, ferritin levels may need to be evaluated alongside markers such as CRP, transferrin saturation, and a complete blood count.
