Ferritin level: normal values and what they mean

Ferritin is a protein that stores iron. Each ferritin molecule can bind and safely store a large number of iron atoms, mainly in the liver, the spleen and the bone marrow. A small fraction of that ferritin leaks into the blood, and that fraction is what the test measures. Your ferritin level is therefore a reflection of how much iron your body has in storage.

That makes ferritin different from the other iron values. Serum iron shows how much iron is circulating in your blood at the moment of the draw, a figure that swings considerably across the day and after a meal. Transferrin is the transport protein that carries iron through the blood, and transferrin saturation indicates what share of that transport capacity is actually occupied. Ferritin answers how much iron you hold in reserve, not how much is in transit.

Results are reported in micrograms per litre (µg/l). The band below is the reference range of the laboratory that performs our tests.

The lower limit sits lower in women because the reference population it was derived from includes menstruating women, who lose iron structurally. It describes what is common in that group. It is not a statement that a smaller reserve is desirable or healthy in women.

Two national bodies, the Dutch society for clinical chemistry and the hereditary haemochromatosis guideline, deliberately decline to publish a universal ferritin reference value. The reason is that the assay differs between laboratories, and the difference is not small: another platform uses 15 to 200 µg/l for men. Both therefore advise using the values of the performing laboratory. Always go by the reference values printed on your own report.

The most important property of ferritin is also the one most often missed: ferritin is an acute-phase protein. With an infection, inflammation, liver damage, heavy alcohol use, obesity, an autoimmune condition or a malignancy, ferritin rises entirely independently of how much iron you actually hold in store. A normal or even high ferritin therefore does not rule out iron deficiency while inflammation is present. This is why ferritin should be assessed together with a CRP as standard: without that second value, a normal ferritin is not reassuring.

The thresholds clinicians use follow that logic. Without inflammation, the World Health Organization treats a ferritin below 15 µg/l in adults as evidence of iron deficiency. Where inflammation is present, the same organisation advises raising the cut-off to 70 µg/l, precisely because inflammation lifts the value artificially. The Dutch GP standard for anaemia works with a third set: below 15 µg/l confirms iron-deficiency anaemia, above 100 µg/l excludes it, and everything between is a grey zone requiring further data.

There is another reason a single value says little. Your iron stores empty before your blood count changes. You can have a clearly reduced ferritin alongside an entirely normal haemoglobin. The literature often cites a clinical cut-off of 30 µg/l for an empty store, with high reliability, and that limit sits noticeably above the 15 µg/l used to establish anaemia. Someone with a low haemoglobin and someone with a normal one can both have a genuine iron deficiency.

This is why ferritin belongs in a panel rather than on its own. The full set is ferritin, serum iron, transferrin, transferrin saturation and CRP. Transferrin saturation is the escape route from the acute-phase trap: a saturation below 20 per cent supports iron deficiency even when ferritin has been pulled up by inflammation. Without that combination, a single ferritin level is mainly a reason for further testing rather than a conclusion.

Ferritin is useful when there are symptoms consistent with an empty iron store: persistent fatigue, breathlessness on exertion, dizziness, hair loss, restless legs or reduced stamina. It is also useful when an earlier blood count already showed something, for example a low haemoglobin or small red cells, and the question is whether iron lies behind it.

The timing of the draw determines how usable the result is, more so than for most other blood values. Because ferritin is an acute-phase protein, any inflammatory response lifts it temporarily. Preferably do not measure within a few weeks of an infection, an operation or a period of heavy physical load. A result taken in such a period can mask a genuine deficiency. If in doubt, have the test repeated once the CRP has returned to normal.

Ferritin itself is not tied to a time of day or a cycle day, and you do not need to fast for it. That differs from serum iron, which does fluctuate across the day and is therefore often drawn in the morning. If the full iron panel is being measured, the morning is the practical choice.

Where possible, request the test together with CRP. Without an inflammatory marker alongside it, a normal or raised ferritin level simply cannot be interpreted, and a second draw becomes necessary anyway.