Ferritin

Ferritin is an iron storage protein found in all cells and can be measured in samples such as serum, plasma, liver and red blood cells. According to the WHO ferritin guideline, low ferritin levels may suggest inadequate iron stores and high levels may suggest iron excess. ^[1]

WHO thresholds

The summary table of the same document gives serum ferritin below 15 µg/L in apparently healthy adults aged 20–59 as iron deficiency, and below 70 µg/L in people with infection or inflammation. The same deficiency thresholds are used in all age groups aged 5 and over; for under 5 the threshold is 12 µg/L. According to the document’s recommendation, 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. ^[1]

Why is it not interpreted on its own?

The WHO states that the ferritin level should be assessed together with indicators of inflammation and infection and, where necessary, adjusted accordingly. ^[1] That is, ferritin can rise during an infection independently of iron stores; the reference range on a laboratory report is also not a single, universal threshold. A single mildly abnormal result is not considered equal in importance to a markedly high or symptomatic situation; decisions belong to the physician’s assessment.

Further reading

For the thresholds of different guidelines and laboratories, the gray zone and high ferritin, see the What should ferritin be? guide; for iron deficiency itself, the Iron guide.