Ferritin
The body's iron storage protein and the best single indicator of total iron stores. It's also an acute-phase reactant, so it rises with inflammation independent of iron status.
Low ferritin causes fatigue, hair loss, poor recovery and reduced training capacity long before hemoglobin drops into frank anemia — one of the most common correctable causes of feeling terrible with 'normal' labs.
Check a Ferritin result against this range →
What Ferritin actually measures — the analyte, and the assay
The protein in your serum is not the protein storing your iron. Tissue ferritin is a 24-subunit hollow shell of heavy and light chains that can hold up to about 4,500 iron atoms in its core, and it sits inside hepatocytes and macrophages. What an immunoassay finds in serum is mostly a light-chain-rich, glycosylated, almost iron-free form that cells actively secrete. Serum ferritin is therefore a secreted signal that correlates with stores, not the stores leaking out — which is precisely why a second input can move it without any iron changing hands.
That second input is transcriptional, and it is the whole story of this page. Ferritin messenger RNA is regulated at two places at once. The iron-responsive element in its 5' untranslated region controls translation according to how much iron the cell holds. Separately, inflammatory cytokines — interleukin-6 and interleukin-1β above all — drive the ferritin promoter directly. Ferritin is a positive acute-phase reactant in the same sense that CRP is, and it will rise on inflammation alone.
The consequence is a whole methodology. The BRINDA project exists because nutrition surveys kept measuring iron status in populations with background inflammation and getting the wrong prevalence; its output is a regression approach that adjusts ferritin using CRP and α-1-acid glycoprotein measured in the same sample Luo 2023. An unadjusted ferritin in an inflamed person is not a conservative estimate of iron status — it is an unknown one.
The measurement itself is a two-site sandwich immunoassay, usually chemiluminescent, calibrated against a WHO international standard. Harmonization between platforms is real but imperfect, so a ferritin of 42 ng/mL at one laboratory and 51 ng/mL at another can be the same blood. And on any streptavidin-based analyzer, high-dose biotin is a live interference: the mechanism is competition for the biotin-binding sites the assay architecture depends on Balzer 2023.
Ferritin: what changes the blood, and what only changes the reading
What changes the ferritin in your blood — ranked, and note that the top two are different phenomena that produce identical numbers:
- Iron stores. The intended signal, and in a person with no inflammation it is a good one.
- Inflammation, at any intensity. Interleukin-6 raises ferritin transcription within a day, and the effect does not require you to feel ill. This is the reason the BRINDA adjustment was built Luo 2023.
- Blood removal. One 450 mL donation takes roughly 200 to 250 mg of iron out of the body in a single sitting — on the order of several months of net dietary absorption — and it does it whether or not the hematocrit needed lowering. In a large population study, 1 in 156 participants carried two copies of the HFE p.C282Y variant, so a minority of donors are drawing down a store that was genuinely overloaded and the rest are not Pilling 2019.
- Hepatic injury and alcohol, which release ferritin from damaged hepatocytes and raise it independently of both iron and cytokines.
- Metabolic dysfunction. Raised ferritin with a normal or near-normal transferrin saturation and no iron-overload genotype now has a name and a consensus definition — metabolic hyperferritinemia — and it is far commoner than hemochromatosis Valenti 2023.
- Hard training. Exercise raises interleukin-6, which raises hepcidin with a peak some hours after the session; in active premenopausal women this interaction is the central complication in reading iron status at all Badenhorst 2022.
What changes only the reading:
- Drawing during or just after an acute-phase response. This is the largest analytical error on the page and it is entirely avoidable: the fix is an hs-CRP in the same tube, every time Luo 2023.
- Which platform ran it, since the between-method spread is wider than the difference many readers are trying to detect.
- High-dose biotin on streptavidin-based analyzers Balzer 2023.
- A hemolyzed sample, which does not belong to the patient at all.
Reference interval or decision threshold — which kind of number Ferritin is
Both kinds of number, at opposite ends of the same interval.
The lower limit is a percentile and it is too low. A printed female lower bound near 15 ng/mL is the 2.5th centile of whoever the laboratory measured — a population that included plenty of iron-deficient women, because iron deficiency is common. When the threshold was instead derived physiologically, by finding the ferritin at which soluble transferrin receptor and hemoglobin start to change, the answer in women of reproductive age who were blood donors came out at ferritin below 25.4 µg/L by transferrin receptor and below 25.3 µg/L by hemoglobin Addo 2022. That is a decision threshold, derived from an outcome, and it sits well above the number most reports flag.
Read that against this site's own audience. The reader most likely to be told their ferritin is ‘normal’ at 18 ng/mL is a woman who menstruates or a man donating blood to hold his hematocrit down — and the donor population is exactly the one the 25 µg/L figure was derived in Addo 2022.
At the top there is no health threshold at all, only a triage number. Nothing is known to happen to you at 300 ng/mL as such. What a high ferritin does is open a differential, and the differential is long: inflammation, alcohol, liver disease, metabolic syndrome, malignancy and, well down the list, genuine iron overload Sandnes 2021. The consensus definition of metabolic hyperferritinemia is built around exactly this — raised ferritin with a transferrin saturation that is not raised, which is what separates a metabolic pattern from an overload one Valenti 2023.
So the honest summary: the bottom of the range is a threshold worth acting on, the top of it is a question, and neither is an optimum. Any specific ‘optimal ferritin’ number quoted for energy or hair is an extrapolation from symptom series, not a value anchored to an outcome in a defined population.
How you would know your Ferritin was wrong — and when to redraw
The retest interval is set by whichever driver you are trying to remove, and there are two of them with very different clocks.
If inflammation is the suspect, wait for the acute-phase response to finish. CRP falls quickly once the stimulus stops; ferritin lags behind it by days, because it is a slower-turnover protein responding to the same cytokines. Practically: at least two to four weeks clear of an infection, a vaccination, a soft-tissue injury or an unusually hard training block, and never during one Luo 2023 Badenhorst 2022.
If repletion is the question, the clock is 8 to 12 weeks, because that is how long it takes absorbed iron to move through erythropoiesis and start accumulating as storage. How you dose changes how much arrives: in iron-depleted women, cumulative fractional absorption was 16.3% on consecutive days against 21.8% on alternate days (p = 0.0013) Stoffel 2017, and the mechanism is that a dose raises hepcidin for roughly a day afterwards and hepcidin blocks the next one Moretti 2015.
Conditions that must match: same laboratory and platform; no acute illness within a month; not within 48 hours of a hard session; and an hs-CRP drawn in the same tube on both occasions, because a ferritin without one is not comparable to anything.
What would have to change for the second value to mean something. A real move in iron stores drags its neighbors with it, and the direction of the discordance tells you which story is true:
- Ferritin up with hs-CRP up? That is the acute phase, not iron. Repeat when the CRP has normalized.
- Ferritin up with hs-CRP flat? Now run the iron panel: a raised transferrin saturation alongside it points at overload and is the trigger for hemochromatosis DNA; a normal saturation points at the metabolic pattern instead Valenti 2023.
- Ferritin falling on iron? Something is still being lost. The CBC and a reticulocyte count show whether the iron is being consumed by erythropoiesis or leaving the body.
- Ferritin up but symptoms unchanged? The symptoms were not iron. That is a real, informative result and it should end the supplementation rather than escalate it.
What Ferritin cannot tell you
On its own it cannot separate a full iron store from an inflamed one. This is not a subtlety at the edges; it is the central limitation, and it is why an entire adjustment methodology had to be invented for population surveys Luo 2023. A ferritin ordered without an hs-CRP beside it answers a question nobody asked.
A normal ferritin does not exclude iron deficiency. In anyone with a live inflammatory process, deficiency hides inside the normal range, and the physiologically derived thresholds sit well above the printed lower limit anyway Addo 2022.
A high ferritin is not iron overload and is usually not hemochromatosis. The saturation is what screens for overload; ferritin is the least specific member of the iron panel and the most commonly over-interpreted Sandnes 2021 Valenti 2023.
It cannot tell you whether your symptoms are iron. Fatigue, hair shedding and poor recovery have many causes and no ferritin value confirms or excludes any of them. The test that answers it is a corrected ferritin with the symptom still present or gone.
The wrong inference readers actually draw comes in two opposite forms. One reads 18 ng/mL as normal because the report did not flag it, when the derived threshold is nearer 25 µg/L and the person is a blood donor Addo 2022. The other reads 480 ng/mL as iron overload and starts donating, when the transferrin saturation was 26% and the real finding was metabolic Valenti 2023.
Sources read for these sections
- Addo OY, et al. Physiologically based serum ferritin thresholds for iron deficiency in women of reproductive age who are blood donors. Blood Advances 2022 · PMID 35404995
- Luo H, et al. A Practical Guide to Adjust Micronutrient Biomarkers for Inflammation Using the BRINDA Method. Journal of Nutrition 2023 · PMID 36792034
- Valenti L, et al. Consensus Statement on the definition and classification of metabolic hyperferritinaemia. Nature Reviews Endocrinology 2023 · PMID 36805052
- Sandnes M, et al. Hyperferritinemia-A Clinical Overview. Journal of Clinical Medicine 2021 · PMID 34067164
- Stoffel NU, et al. Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials. Lancet Haematology 2017 · PMID 29032957
- Moretti D, et al. Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women. Blood 2015 · PMID 26289639
- Badenhorst CE, et al. A contemporary understanding of iron metabolism in active premenopausal females. Frontiers in Sports and Active Living 2022 · PMID 35966107
- Pilling LC, et al. Common conditions associated with hereditary haemochromatosis genetic variants: cohort study in UK Biobank. BMJ 2019 · PMID 30651232
- Balzer AHA, et al. An Analysis of the Biotin-(Strept)avidin System in Immunoassays: Interference and Mitigation Strategies. Current Issues in Molecular Biology 2023 · PMID 37998726
The plan of attack
In this order. Most people start at step four, which is why they change five things at once and learn nothing.
- Confirm the number is real
An iron supplement taken before the draw. Oral iron raises serum iron and transferrin saturation for hours afterwards, which makes a deficiency panel read better than the person is. Ferritin itself moves more slowly, so the panel becomes internally inconsistent. Hold iron for 24 hours before the draw, and take the sample fasted in the morning. - Read it with its partner
Pair with the Iron Panel and hs-CRP for a complete and correctly interpreted picture. Draw it alongside: Complete Blood Count (CBC) with Differential, Iron Panel (Iron, TIBC, Transferrin Saturation), hs-CRP (High-Sensitivity C-Reactive Protein). - Work out which direction is yours
If it's high — Always interpret next to hs-CRP — inflammation raises ferritin independent of iron. Persistently high ferritin with high transferrin saturation warrants hemochromatosis genetic testing.
If it's low — Fatigue, hair shedding, cold intolerance, restless legs, poor endurance, low mood. - Fix it in this order
Nutrition. Red meat and liver are the most bioavailable sources (heme iron). Pair plant iron with vitamin C. Separate iron from coffee, tea, calcium and zinc by 2 hours — these substantially inhibit absorption.
Lifestyle. Investigate the cause of loss — heavy periods, GI bleeding, or over-donation. In men, unexplained iron deficiency warrants GI evaluation.
Supplements. Iron bisglycinate every other day — alternate-day dosing produces better absorption than daily, because daily dosing raises hepcidin and blocks uptake. Take with vitamin C on an empty stomach if tolerated. Retest before continuing long-term.
Hormones. Treat heavy menstrual bleeding (a gynecological conversation). If donating blood for hematocrit control, space donations and monitor ferritin.
Compounds. The classic TRT trap: donate blood repeatedly to control hematocrit → tank ferritin → feel exhausted → blame testosterone. Track both together, always.
Work down the list, not across it. Adding a compound on top of an unfixed diet is why generic protocols fail. - Retest
8–12 weeks after starting iron; every 6 months if donating blood. Change one thing at a time, or the retest can't tell you which thing worked.
How to fix it
📚 WHO ferritin threshold guideline. Camaschella C, NEJM 2015 — iron-deficiency anemia. Stoffel NU et al., Lancet Hematol 2017 — alternate-day iron dosing.
This page can tell you what could have made your Ferritin wrong. It cannot tell you whether it did.
Everything above is free and stays free — the assay, what changes the reading rather than the blood, the retest window and the sources. What no page can do is look at your draw: which laboratory ran it, at what hour, what you were taking that week, and what else was flagged beside it. Every one of those changes the answer, and none of them is on any page. Bringing a real result to people who know that list is what the members' area is for.
Bring your result — $10/mo →🩸 Test your Ferritin
Order directly through Marek Diagnostics — no doctor's visit needed, drawn at any Quest location in the US. Code CAMERON applies 10% off automatically.
Order this test — 10% off → Browse all 103 markers →What Ferritin is usually tested alongside
One marker is a data point. These panels add the markers that make Ferritin interpretable, name why each is on the list, and load the set into your cart at 10% off.
includes this + 11 more markers — Persistently exhausted despite adequate sleep, and either haven't been tested or were told everything is normal.
includes this + 6 more markers · built for men — Never had proper bloodwork, or want the highest-value snapshot for the least money.
includes this + 6 more markers · built for women — Exhausted, breathless on stairs, hair shedding, brittle nails, restless legs, brain fog — and you've been told your blood count is normal. Extremely common in menstruating women, endurance athletes, and anyone plant-based.
includes this + 9 more markers · built for women — Widening part, thinning at the crown, more hair in the shower drain, or a ponytail that's visibly thinner than it was.
What people use Ferritin to decide
Nobody orders a test for its own sake. Ferritin is on the test list for these pathways — each one links to what the pathway claims, and what its test list is read for before you spend anything on it.
Repair capacity is systemic. Persistently raised CRP means you're accumulating damage faster than you clear it, and low vitamin D or ferritin blunt recovery long before they show up as a diagnosis.
The unglamorous checks that explain most stalled progress. Low ferritin and low B12 both present as 'I just can't train hard any more' with a completely normal full blood count.
The highest-yield test on this whole page. Ferritin under 30 impairs endurance well before hemoglobin drops, so the full blood count reads normal while performance falls off a cliff — and it is disproportionately common in women and plant-based athletes.
Iron is a cofactor for tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis. Low ferritin presents as no motivation and no drive, and it gets treated as depression far more often than it gets tested.
Ferritin is also on the test list for these, where it narrows the picture rather than settling it:
What's keeping you awake — the upstream causes · Circadian & melatonergic rhythm · Sleep depth, slow-wave & recovery quality
Hair — follicle biology & the androgen problem · Pigment, tone & photoprotection
Motility, IBS & the brain-gut axis · Barrier integrity & mucosal repair · Digestive output — acid, enzymes & bile
The short list — highest probability of mattering · Test before you guess
What moves your Ferritin
3 compounds and 11 supplements in the Vault have a documented effect on this marker, or are a reason to have measured it first:
Browse all 278 compounds & 371 supplements →
Would you feel it? Symptoms Ferritin helps explain
People search for how they feel, not for a marker. These are the complaints where this one is worth checking, and whether it is first-line or a follow-up.
Why your Ferritin might be wrong
Most abnormal results are interference, not disease. Check these before you change anything. Each says whether the number is wrong (repeat it), badly timed (redraw it), or real with a cause.
Oral iron raises serum iron and transferrin saturation for hours afterwards, which makes a deficiency panel read better than the person is. Ferritin itself moves more slowly, so the panel becomes internally inconsistent.
Hold iron for 24 hours before the draw, and take the sample fasted in the morning.
Ferritin is an acute-phase reactant. Inflammation drives it UP independently of iron stores, so a normal-looking ferritin can sit on top of genuine iron deficiency. A recent illness, an injury, or a heavy training block all do it.
Read ferritin next to hs-CRP. If CRP is up, the ferritin is not trustworthy as an iron measure — repeat both once the inflammation settles.
Ferritin is an acute-phase reactant as well as an iron store. Infection, injury, obesity, hard training and liver stress all raise it — so a 'normal' ferritin of 60 alongside a CRP of 8 may be a depleted ferritin of 20 wearing a disguise. This is the single most consequential interference in the whole Vault, because it causes real iron deficiency to be missed.
Never read ferritin without a CRP beside it. If CRP is up, lean on transferrin saturation instead.
Rises acutely for days after hard exercise, which produces a falsely reassuring number in exactly the athletes most likely to be deficient.
Draw at least 48–72 hours after a hard session.
Recent dosing raises measured ferritin above your true stored level — supplemental iron shows up in the tank before it has actually filled it.
Stop iron 5–7 days before a draw meant to assess your baseline.
Lowers ferritin substantially; can falsely lower HbA1c by shortening red cell lifespan.
Track ferritin every time you donate — the classic TRT trap. Note recent donation when reading HbA1c.
Raises inflammatory markers and ferritin; suppresses testosterone and T3 (nonthyroidal illness).
Wait 2–4 weeks after an illness before drawing — otherwise you're measuring the infection, not your baseline.
What Ferritin means in combination
One marker tells you a little; combinations tell you the story. These are the named patterns this one takes part in.
Low energy availability shuts the reproductive axis down to save fuel. It is not a badge of being lean — it costs bone density in a way that does not fully come back.
Eat more. That is the treatment, and no supplement substitutes for it. Get bone density assessed if it has been going on for a year or more. The RED-S panel exists for exactly this picture.
Female pattern shedding is very often nutritional and thyroidal before it is hormonal. Each of these alone can shed hair; together they reliably do.
Ferritin above 50 is the usual threshold for regrowth — normal is not the same as sufficient here. Fix all three and give it 3–6 months; the hair cycle is slow and nothing shows in weeks.
Converting T4 into active T3 needs selenium, iron, zinc and adequate energy. When those are short — or under stress and illness — you make inactive reverse T3 instead.
Adding more T4 to a conversion problem does not work. Correct ferritin and selenium first, address energy availability and stress, and retest in 8–12 weeks before changing any thyroid medication.
The classic TRT trap. Repeated phlebotomy to control hematocrit depletes iron stores. You fixed the viscosity and created iron-deficiency fatigue.
Track ferritin every time you donate. Supplement iron (bisglycinate, alternate-day dosing absorbs better) and re-evaluate whether the TRT dose/frequency itself is driving the hematocrit up.
What to test next
These put Ferritin in context — each with its own full breakdown.
Frequently asked questions
30–400 ng/mL. Ranges vary by laboratory and assay — always compare to the range printed on your own report.
>50 ng/mL minimum; ~75–150 ng/mL for energy and hair.
Always interpret next to hs-CRP — inflammation raises ferritin independent of iron. Persistently high ferritin with high transferrin saturation warrants hemochromatosis genetic testing.
Fatigue, hair shedding, cold intolerance, restless legs, poor endurance, low mood.
You can order Ferritin directly through Marek Diagnostics without a doctor's visit — drawn at any Quest Diagnostics location in the US. Code CAMERON applies 10% off automatically.
Where this goes next
This page is the free framework, and it splits by sex. The protocol itself — the dosing, the order to correct things in, the week-by-week schedule and what to retest — is a lesson inside Skool.