Ferritin levels

What is ferritin and what does it show?

Ferritin is an iron storage protein found in all cells; it can be measured in serum, plasma and other samples. In the absence of inflammation, the ferritin level in the blood is directly proportional to total body iron stores: it falls in iron deficiency and rises in iron overload. ^[1]

The NIH describes ferritin as currently the most effective and cost-effective test for identifying iron deficiency. Because it falls in the first stage, when the stores are decreasing, it can show low iron status even while hemoglobin is still normal. ^[2]

Ferritin has an important limitation: it is an acute-phase protein. In conditions such as infection, inflammation, liver disease, obesity and cancer, ferritin can be normal or high even when the stores are empty. ^[1]

What should ferritin be? Thresholds by organization

The threshold varies with who sets it and for what purpose. The WHO values are defined for both individuals and population screening; the NIH and BSG values describe clinical interpretation; the AASM values are only for the treatment of restless legs syndrome.

Three conclusions follow from the table. First, below 15 µg/L means deficiency in almost all sources; the BSG gives the specificity of this threshold as 0.99. Second, 15–30 µg/L is a gray zone: the BSG states that the lower limit of most laboratories is in this range, while the NIH states that below 30 µg/L suggests deficiency. The same result may be considered “normal” in one laboratory and “low” in one guideline. Third, higher ferritin does not mean better; thresholds such as the 75 ng/mL used for restless legs are specific to that condition. ^[3]

For ferritin, 1 ng/mL equals 1 µg/L; laboratory reports use one of the two units and the numbers can be compared directly.

What does low ferritin mean?

According to the BSG, in the absence of inflammation, ferritin is the most specific test for iron deficiency. Low ferritin shows that iron stores are depleted; this can also be at a stage before iron deficiency anemia has developed. ^[3]

Low ferritin is the beginning of a diagnosis, not its end. The cause may be heavy menstrual bleeding, blood loss from the digestive tract, frequent blood donation, malabsorption problems such as celiac disease, pregnancy or a predominantly plant-based diet. The BSG states that values below 45 µg/L may call for consideration of investigation of the digestive tract, particularly if there is chronic inflammatory disease together with anemia. ^[3]

When low ferritin is found, hemoglobin is also assessed: if hemoglobin is normal, it is iron deficiency without anemia; if low, it is iron deficiency anemia.

Can ferritin be normal and iron deficiency still be present?

Yes. The WHO states that in people with infection or inflammation, ferritin below 30 µg/L under age 5 and below 70 µg/L in older people and adults may indicate iron deficiency (conditional recommendation, low-certainty evidence). The WHO also recommends measuring ferritin together with two acute-phase proteins, CRP and AGP, in regions where infection or inflammation is common. ^[1]

The BSG states that, when ferritin is suspected to be misleadingly normal, tests such as transferrin saturation may help. Other indicators of iron deficiency listed by the guideline include low serum iron, high total iron-binding capacity, high soluble transferrin receptor (sTfR), low reticulocyte hemoglobin and a high percentage of hypochromic red cells. According to the BSG, ferritin above 150 µg/L, even in the presence of inflammation, is hardly compatible with absolute iron deficiency. ^[3]

A good response to iron treatment in a patient with anemia also helps the diagnosis: the BSG states that a rise in hemoglobin of at least 10 g/L (1 g/dL) within 2 weeks of iron treatment strongly suggests absolute iron deficiency even when iron tests are inconclusive. ^[3]

What does high ferritin mean?

According to the WHO 2020 guideline, in otherwise healthy people, ferritin above 150 µg/L in menstruating women and above 200 µg/L in men and non-menstruating women may point to a risk of iron overload. In unhealthy adults this limit is 500 µg/L. The guideline recommends that ferritin not be used alone to determine the risk of iron overload, and that people with high ferritin undergo clinical and laboratory evaluation to find the underlying cause. ^[1]

The review by Sandnes and colleagues estimates that only about 10% of high-ferritin cases in routine medical practice are associated with iron overload. In the rest, ferritin is raised reactively due to a cause such as inflammation, metabolic syndrome, chronic alcohol use, cell damage or cancer. ^[4]

Transferrin saturation is useful in distinguishing iron overload. According to the review, above 45% in women and above 50% in men is generally considered high; however, a normal saturation does not always exclude iron overload. In about one third of patients with fatty liver and metabolic syndrome, body iron stores are increased (dysmetabolic iron overload syndrome); in these patients transferrin saturation is mostly normal. ^[4] HFE hemochromatosis is the most common single-gene disease in northern European populations; it is much rarer in other populations. ^[4]

High ferritin is therefore not a diagnosis but a finding whose cause is to be investigated. As the WHO stresses, the result is interpreted together with clinical assessment and additional laboratory tests. ^[1]

Why can laboratory results differ?

The WHO states that ferritin can be measured by different methods (radiometric, non-radiometric and agglutination assays) and that, when calibrated with a material traceable to the WHO international reference standard, none of the methods appears superior to another. The guideline recommends that, once a method is chosen, the same method be used in follow-up of a person. ^[1]

Small differences between two measurements made in different laboratories may therefore not show a real change. The reference range next to the report is laboratory-specific; the BSG states that the lower limit of most laboratories is in the 15–30 µg/L range. ^[3]

In the assessment of restless legs syndrome, the AASM recommends that ferritin and transferrin saturation testing preferably be done in the morning, after avoiding iron-containing supplements and foods for at least 24 hours beforehand. This recommendation is written in the RLS context. ^[5]

How common is low ferritin in Türkiye?

A 2020 report by Ministry of Health experts states, according to Türkiye Nutrition and Health Survey (TBSA) 2010 data, that low serum ferritin was most common in women aged 31–50 (47.5%) and 19–30 (47.4%). In the 2011 Gazi University study cited in the report, low ferritin was found in 43.7% of the mothers of children aged 6–17 months and in 28.7% of the children. ^[6]

These proportions show that low ferritin may be common, particularly in women of reproductive age. However, the ferritin thresholds used in the report are not stated and the data belong to 2010–2011; they cannot be read as a current, single national rate.

This page does not make a diagnosis or recommend personal doses. The ferritin result is interpreted by a physician together with hemoglobin, CRP, transferrin saturation, symptoms and history.