Where Your Lab's Ferritin Floor Actually Came From
Eighteen of twenty-three North American laboratories surveyed print a lower limit for ferritin in women that sits below the cutoff clinical guidelines recommend — and the method used to build those limits includes people who were themselves iron depleted.
The case file
- Revising Ferritin Lower Limits: It's Time to Raise the Bar on Iron DeficiencyJournal of Applied Laboratory Medicine — survey of clinical laboratories across North America · 202118 of 23 responding laboratories reported female lower limits well below 15 µg/L, while clinical guidelines recommend 15 or 30.
- Re-evaluating ferritin thresholds to diagnose iron deficiencyClinical Biochemistry · 2025Reference intervals are frequently lower than evidence-based recommendations, and including asymptomatic iron-depleted people in the reference population likely explains why.
- Serum or plasma ferritin concentration as an index of iron deficiency and overloadCochrane Database of Systematic Reviews · 2021Ferritin is an acute-phase protein: inflammation and infection push it up, independently of how much iron you have.
I went looking for where the number came from.
Not the ferritin result — the other number, the small one in brackets beside it, the one that decides whether anybody in the room says anything. On most printouts for women it starts somewhere between 10 and 15. I wanted to know who chose it.
The answer is in the laboratory medicine literature, written by laboratory people, and it is worse than I expected.
"Normal" is a statistical statement, not a clinical one
A reference interval is built by measuring a group of people considered healthy and drawing a line that captures most of them. It is a description of a sample. It was never a statement that everyone inside it has enough iron.
This matters because of what the sentence "your ferritin is normal" does in a ten-minute appointment. It ends the conversation. Not because anyone decided your iron was adequate, but because the value fell inside a band computed from other people.
The reference population included people who were already short of iron
This is the part that should be better known.
A 2025 paper in Clinical Biochemistry states it plainly: sex-specific reference intervals for ferritin are frequently lower than evidence-based recommendations, and the inclusion of asymptomatic, iron-depleted individuals in reference-interval studies likely accounts for those inappropriate thresholds 2.
Read that again with the mechanism in view. You recruit women from the general population, call them healthy because nothing has been diagnosed, and measure their ferritin. A large share of them are quietly iron depleted — menstruating, not supplementing, nobody has ever checked. Their low values go into the pool. The pool sets the floor. The floor is now low enough to call them normal.
The deficiency builds its own permission slip. The same paper notes that an expert consensus panel has proposed a lower cutoff of 30 µg/L instead 2.
Eighteen out of twenty-three
In 2021 the Journal of Applied Laboratory Medicine surveyed clinical laboratories across North America and asked what reference intervals they report with a ferritin result. Of 23 that responded, 18 reported female lower limits well below 15 µg/L — while the clinical guidelines those same laboratories work alongside recommend cutoffs of 15 or 30 µg/L for uncomplicated iron deficiency 1.
The same group then looked at 52,027 patient ferritin values collected over five years. In that population, the cutoff that identified iron deficiency anaemia at the 90th percentile was 24 µg/L in women 1. Not 10. Not 12.
Two details from that dataset stayed with me. Median ferritin rose two- to threefold after menopause 1 — so a single female range covers two populations that are not comparable. And when the authors sorted female patients by the specialty that ordered the test, the highest prevalence of low ferritin was in obstetrics and gynaecology 1. The women most likely to be depleted are being measured against a range partly built from women like them.
The number can also be wrong in the other direction
There is a second failure mode, and it runs the opposite way.
Ferritin is an acute-phase protein. Inflammation and infection raise it independently of iron stores 3. A woman with a persistent inflammatory process can carry a mid-range ferritin and empty stores at the same time, and the result will look reassuring.
Nobody in the room is the villain, and that is the indictment
The laboratory is doing exactly what it was asked to do. A reference interval is a statistical product; producing one from a sampled population is correct practice. The laboratory was never asked "at what level do women stop feeling ill", so it did not answer that question.
The clinician is reading forty results an hour on a screen that flags what falls outside the band. Your value was not flagged. There is no mechanism in that workflow for interrogating where the band came from, and no time to.
So a number assembled from partly depleted women, for a purpose other than yours, gets used to close your appointment. No malice anywhere in the chain, and the outcome is the same as if there had been. The people who documented this discrepancy are laboratory scientists themselves 1 2 — this is not an outsider's complaint, it is an open argument inside the field that has not yet reached the printout you were handed.
What to do with this
- Ask for the number, not the verdict. "What was my ferritin?" gets you a figure; "are my levels okay?" gets you the band.
- Write down the lower limit your laboratory uses, next to your result. That one line tells you which argument you are actually in.
- If your value sits between your lab's floor and 30 µg/L, the sentence that moves things is specific: guidelines recommend cutoffs of 15 or 30 µg/L for uncomplicated iron deficiency 1, and I would like to know which applies to me.
- If you have symptoms and a mid-range ferritin, ask whether inflammation could be raising it, and whether an inflammatory marker should be checked alongside.
- If you are postmenopausal, know that the single female range covers two populations: median ferritin rises two- to threefold after menopause 1.
Questions people also ask
Is a ferritin of 14 normal?
It is inside the printed range at most laboratories, and below the cutoff clinical guidelines recommend. A 2021 survey found 18 of 23 North American laboratories reporting female lower limits well below 15 µg/L, against guideline cutoffs of 15 or 30 1. Both statements are true at once, which is the whole problem.
Why do reference ranges differ between laboratories?
Because each is derived from its own reference population and method rather than from a shared clinical threshold. That is why the same result can be flagged in one laboratory and not in another, and why the lower limit is worth writing down.
Can my ferritin look fine while my iron stores are empty?
Yes. Ferritin is an acute-phase protein, and inflammation or infection raises it independently of iron stores 3. A mid-range value in someone with symptoms and ongoing inflammation is not reassurance on its own.
Does this mean my doctor was wrong?
It means the band on the printout was not built to answer the question you came in with, and the workflow gives nobody time to notice. The useful move is not an argument about who was wrong; it is bringing the specific number and the specific guideline cutoff into the next appointment.
Sources
Every number above comes from one of these. Each carries its PMID, the number it is filed under in the US National Library of Medicine, if you want to look it up yourself.
- Revising Ferritin Lower Limits: It's Time to Raise the Bar on Iron Deficiency.
- Re-evaluating ferritin thresholds to diagnose iron deficiency.
- Serum or plasma ferritin concentration as an index of iron deficiency and overload.
This article is information, not medical advice, diagnosis or treatment. Reference ranges, doses and protocols differ between people and between laboratories. Talk to a qualified clinician before changing anything about your care.