How this instrument works
Ferritin is the protein the body uses to store iron, and a low reading is normally a strong sign that iron stores are running low. The WHO's screening cutoffs split by two things: age (under 5, or 5 and older) and whether inflammation or infection is currently active. Without inflammation, the cutoff is 12 ng/mL under age 5 and 15 ng/mL from age 5 up. With inflammation present, the cutoffs both rise, but not to the same number — 30 ng/mL under age 5, and a higher 70 ng/mL from age 5 up. A ferritin reading below the applicable cutoff flags likely iron deficiency; at or above it, this screen doesn't flag deficiency.
The reason for the split is that ferritin is an acute-phase reactant — its level rises during inflammation or infection for reasons that have nothing to do with how much iron is actually stored. A person with genuinely low iron stores who also has an infection can produce enough extra ferritin from the inflammation alone to land in a range that looks reassuringly normal against the ordinary no-inflammation cutoff, even though their iron stores are still low. Raising the cutoff when inflammation is present corrects for that inflation, catching cases the flat cutoff would otherwise miss — and the WHO sets that raised cutoff differently for young children than for everyone else, rather than using one inflammation-adjusted number across all ages.
This is a screening check built on one lab value and two simple facts, not a diagnosis. Confirming genuine iron deficiency in a clinical setting usually calls for a fuller iron panel — transferrin saturation, total iron-binding capacity, sometimes a reticulocyte count — read alongside symptoms, diet, and history of blood loss. A result from this calculator is a reason to ask a clinician for that fuller workup, not a stand-in for it.
- Enter the serum ferritin result in ng/mL.
- Enter age in years — the cutoff changes at the under-5 threshold.
- Set inflammation or active infection to Yes if any is currently present, No otherwise.
- Read the cutoff applied and whether the ferritin falls below it.
Worked example — same ferritin, different age and inflammation status
A 30-year-old with a ferritin of 10 ng/mL and no active inflammation is compared against the 15 ng/mL cutoff for that age group. 10 is below 15, so this screen flags likely deficiency.
That same person's 40 ng/mL ferritin, if it occurred alongside active inflammation, would be compared against a 70 ng/mL cutoff instead — the adult inflammation-adjusted threshold — and would still fall below it, flagging deficiency despite the far higher raw number.
A 3-year-old with a ferritin of 20 ng/mL and no inflammation is compared against the under-5 cutoff of 12, falls above it, and isn't flagged. But a 4-year-old with a ferritin of 25 ng/mL and active inflammation is compared against the under-5 inflammation cutoff of 30 — lower than the 70 ng/mL adult inflammation cutoff — and 25 falls below it, flagging deficiency.
Questions
Why does ferritin need a different cutoff depending on inflammation status?
Because ferritin is an acute-phase reactant — its blood level rises during inflammation or infection regardless of how much iron is actually stored in the body. That means a person with true iron deficiency who also has active inflammation can show a ferritin reading that looks falsely normal, or even elevated, against the plain no-inflammation cutoff. The WHO's higher inflammation-adjusted cutoffs — 30 ng/mL under age 5, 70 ng/mL from age 5 up — exist specifically to catch those cases rather than mistake an inflammation-inflated number for adequate iron stores.
Is this calculator diagnosing iron deficiency?
No — it's a screening check based on one lab value and two facts about the person. A genuine diagnosis of iron deficiency is confirmed with a fuller iron panel and the clinical picture: symptoms, diet, menstrual or gastrointestinal blood loss, and often additional labs like transferrin saturation. Treat a flagged result here as a reason to pursue that fuller evaluation, not as a finished answer.
Why is the cutoff different for children under 5?
Ferritin levels and iron requirements both differ across early childhood as a matter of normal physiology, so the WHO set separate, lower cutoffs for children under 5 rather than applying the same numbers used from age 5 onward — 12 ng/mL instead of 15 ng/mL without inflammation, and 30 ng/mL instead of 70 ng/mL with inflammation. Age 5 and up, including all adults, share the same pair of thresholds.
Why is the inflammation-adjusted cutoff lower for young children than for adults?
The WHO's 2020 guideline sets 30 ng/mL as the inflammation-adjusted cutoff for children under 5, well below the 70 ng/mL used from age 5 up. It isn't simply the child version of the same adjustment — the two age groups get genuinely different inflammation-adjusted numbers, reflecting how ferritin and inflammatory response both differ in young children.
What causes the kind of inflammation that would raise this cutoff?
Anything that triggers an acute-phase immune response — a current infection, a recent illness, chronic inflammatory conditions, even significant recent tissue injury — can push ferritin up independent of iron status. If any of that is active when the blood was drawn, the inflammation-adjusted cutoff for that age group is the more appropriate comparison than the plain, no-inflammation cutoff.
Can ferritin be elevated even when someone is genuinely iron-deficient?
Yes, and that's the exact problem the inflammation-adjusted cutoffs are designed to catch. A person with real iron deficiency but a concurrent infection can have inflammation add enough extra ferritin to push the reading well above the plain cutoff, even into a range that superficially looks fine — only the higher, inflammation-aware cutoff for their age group still correctly flags it. This is one of the clearest reasons ferritin is never read in isolation.
Where does the WHO's 2020 guideline apply these cutoffs?
The guideline covers both individual clinical screening and population-level surveys of iron status, and it's built on a systematic review of how ferritin relates to iron stores across age groups and inflammation states. It replaced older, less age-specific ferritin cutoffs with the four-way, age- and inflammation-stratified version used in this calculator.
References
- World Health Organization, 2020 — WHO guideline on use of ferritin concentrations to assess iron status (NCBI Bookshelf)
- NIH Office of Dietary Supplements — Iron, Health Professional Fact Sheet
Read this first: This instrument computes a screening figure from population formulas — it is not a diagnosis, and it cannot see the whole picture a clinician can. Use it to inform a conversation, not to replace one.