Ferritin

A protein that reflects your iron stores — low means iron deficiency, but inflammation pushes it up, so a “normal” value can hide a deficiency.

What it measures

The blood level of ferritin, an indirect proxy for your total body iron stores.

Why it matters

It’s the single best blood test for iron deficiency — but it’s also an “acute-phase reactant” that rises with infection, inflammation, liver disease and cancer, which can mask a real deficiency.

Healthy target

Deficiency below ~30 µg/L (WHO uses < 15; raise the cut-off to ~70 if inflammation is present). Genuinely debated.

How to read your value

A normal or high ferritin does NOT rule out iron deficiency if you have inflammation — it should be read with a marker like CRP and your clinical picture. Persistently very high ferritin points to inflammation or iron overload (e.g. haemochromatosis), not “great iron stores”.

What can affect it

• Inflammation or infection (raises it independently of iron)
• Liver disease and alcohol
• Recent iron intake
• True iron overload

Does the target differ by age or sex?

Reference ranges run lower for women than men — but that partly reflects that many women simply have depleted stores, not a different healthy “normal”. Thresholds also shift with age.

When to talk to a clinician

Low ferritin should prompt a search for the cause of iron loss; unexplained high ferritin should be evaluated for inflammation or iron overload.