Explainer · updated 2026-09-09

Ferritin, explained in plain English

Written by the medk.AI team · Last reviewed September 2026 by the medk.AI content team

Key facts

• Typical adult reference interval in men: 24-336 ng/mL (ABIM)
• Typical adult reference interval in women: 24-307 ng/mL (ABIM)
• Cutoff WHO uses to judge low iron stores when infection or inflammation is present: 70 µg/L (WHO 2020)
• What ferritin measures: the body's iron reserve, which falls before anaemia shows up and is raised by inflammation (WHO 2020)

What it is

Ferritin is a protein that stores iron. The number on your report reflects the iron your body keeps in reserve. That distinction matters, because ferritin often changes before anything else on the page does. It is measured in the blood, and it can fall before anaemia shows up, which makes it one of the earliest warnings that iron stores are running down. Inflammation raises it as well.

What the number is telling you

The test reflects the iron your body keeps in reserve, and it often moves before other results do. One value on its own says little; tracked over time, it starts to mean something. Ferritin is read together with the other iron results on the report, and the story is in how the set moves, not in any single line.

What high or low can mean

Low usually means the reserve is running down. It is often the earliest sign on the report. Where infection or inflammation is present, WHO judges low iron stores against a higher cutoff of 70 µg/L.

High is less specific. The stores may simply be full, but infection and inflammation raise ferritin too, so a high reading is read beside an inflammation marker. One high reading on its own settles nothing; it tells your doctor where to look next.

What a typical result looks like

Typical adult reference intervals from ABIM run from 24 to 336 ng/mL in men and from 24 to 307 ng/mL in women. The range on your own report is the one that counts.

Questions worth asking your doctor

• Was this measured while I was ill or inflamed?
• How does it compare with my previous results?
• Do my other iron tests tell the same story?
• If my level is low, should we look for a source of blood loss?

If a result worries you, ask your doctor.

Sources

• WHO guideline on use of ferritin concentrations to assess iron status in individuals and populations (2020)
• ABIM Laboratory Test Reference Ranges (2026)