Ferritin

The main iron storage protein, and the first test for iron deficiency, with the important catch that inflammation raises it independently of iron status.

What it measures

Ferritin is the protein cells use to store iron safely. Circulating ferritin correlates with total body iron stores, which is why it is the first line test for iron deficiency and generally more informative than serum iron.

It is also an acute phase reactant. Infection, injury, liver disease, obesity related inflammation and heavy training all raise it, which can mask genuine deficiency.

Thresholds and the inflammation problem

WHO guidance places iron deficiency in adults below 15 micrograms per liter, and raises the threshold to below 70 in the presence of infection or inflammation. Many clinicians use a higher functional cutoff, particularly in people with fatigue, hair loss or heavy menstrual bleeding, because symptoms often appear before the formal threshold is crossed.

This is why ferritin is read alongside CRP, transferrin saturation and a blood count rather than alone. A normal ferritin with a high CRP does not rule out deficiency.

When it is high

High ferritin is usually inflammation, alcohol intake, metabolic dysfunction associated fatty liver disease or obesity, not iron overload. It can also indicate hereditary hemochromatosis, which is why a genuinely elevated result with a high transferrin saturation warrants follow-up rather than reassurance.

Iron supplementation without a confirmed deficiency is not benign, and ferritin is the number that decides.

Reference ranges

  • Iron deficiency, adults: below 15 micrograms/L. WHO 2020 guidance on ferritin concentrations for assessing iron status.
  • Iron deficiency with inflammation or infection: below 70 micrograms/L. WHO 2020. Higher threshold applied because inflammation raises ferritin.

Ferritin is one of the markers we recommend, ideally read alongside CRP and a blood count rather than in isolation.

References

  1. World Health Organization. WHO guideline on use of ferritin concentrations to assess iron status in individuals and populations. 2020.
  2. Camaschella C. Iron deficiency. Blood. 2019.
  3. Adams PC, Barton JC. A diagnostic approach to hyperferritinemia with a non-elevated transferrin saturation. J Hepatol. 2011.