You have your result in front of you: ferritin 18 µg/L, or 25, or 38. Next to it, the reference range from the laboratory, which sometimes starts at 10. And that sentence many hear: "it's within normal limits." Yet fatigue is there, hair is falling out, climbing stairs leaves you breathless. So, low ferritin or not?
This article answers this specific question: what ferritin actually measures, the thresholds validated by research (and why they differ from the "norms" printed on your report), symptoms of low ferritin without anemia, the inflammation trap, causes, and the protocol to raise it. It's the practical complement to our complete iron deficiency guide.
14 mg of iron chelated to glycine (100% of NRV) with 80 mg of vitamin C for absorption and 200 µg of vitamin B9. One vegetable capsule per day, with no metallic taste. Made in France.
Ferritin reflects iron reserves. Below 15 µg/L, they are depleted; below 30 µg/L, deficiency is highly probable (Cochrane review 2021: 98% specificity at this threshold); with fatigue or hair loss, most doctors aim for above 50. Laboratory "normal" ranges often start at 10–15, a value corresponding to an iron-depleted bone marrow. Low ferritin corrects in 3 to 6 months, after identifying the cause, with a well-absorbed form of iron taken in the morning, away from tea, coffee, and dairy products. If CRP is elevated, ferritin may appear normal despite true deficiency.
- Ferritin: what this number really measures
- Low ferritin: the thresholds that matter
- Symptoms of low ferritin without anemia
- Low ferritin, normal hemoglobin: why take action
- "Normal" ferritin but deficient: the inflammation trap
- Causes of low ferritin
- How to raise your ferritin
- When to consult without delay
- Frequently Asked Questions
1. Ferritin: what this number really measures
The body stores its iron reserves in a hollow protein, called ferritin, which can hold up to 4,500 iron atoms. A small fraction circulates in the blood, and its concentration faithfully tracks the state of reserves: 1 µg/L of ferritin corresponds, roughly, to 8 to 10 mg of stored iron. This is why ferritin drops first, weeks or months before hemoglobin, and why it is the reference test for detecting deficiency at its earliest stage (Camaschella, Blood, 2019).
What ferritin doesn't tell you: it measures neither iron in circulation nor iron available to tissues. And most importantly, it is part of the so-called "acute phase" proteins: any inflammation raises it, regardless of reserves. We return to this at section 5, because it's the number one source of error.
2. Low ferritin: the thresholds that matter
Reference ranges printed on results are calculated statistically from a laboratory population, some of which are themselves deficient. They don't say "healthy," they say "common." The thresholds that matter come from studies that compared blood ferritin to the absolute reference: the amount of iron visible in bone marrow.
In healthy individuals, median ferritin was 15.1 µg/L when bone marrow contained no iron, and 70.4 µg/L when reserves were present. The authors confirm the validity of WHO thresholds for healthy populations.
Garcia-Casal MN, et al. Arch Med Res 2018;49(6):405-417. DOI: 10.1016/j.arcmed.2018.12.005
In adults presenting with a health problem, a ferritin threshold set at 30 µg/L detects 79% of iron deficiencies with 98% specificity. The diagnostic likelihood ratio of 140 makes it a highly informative test.
Garcia-Casal MN, Pasricha SR, et al. Cochrane Database Syst Rev 2021;5:CD011817. DOI: 10.1002/14651858.CD011817.pub2
| Ferritin (µg/L) | Interpretation | Context |
|---|---|---|
| Less than 15 | Reserves depleted, definite deficiency | WHO threshold, corresponds to iron-empty bone marrow |
| 15 to 30 | Deficiency highly probable | Standard clinical threshold (Cochrane 2021, Lancet 2021). Often "within laboratory normal ranges" |
| 30 to 50 | Low reserves | With fatigue, hair loss, or intense exercise, correction is justified (Vaucher 2012) |
| 50 to 75 | Adequate reserves | Except restless legs, where recommendations aim for above 75 |
| Less than 100 with elevated CRP | Possible deficiency despite a "normal" number | Request transferrin saturation coefficient (Cappellini 2017) |
| More than 300 (women) or 400 (men) | Excess or inflammation | No supplementation; medical advice (hemochromatosis to be ruled out) |
Indicative reference values for adults, excluding pregnancy and chronic disease. Final interpretation is the physician's responsibility.
3. Symptoms of low ferritin without anemia
Two-thirds of iron is used to make hemoglobin, but the rest powers the enzymes of energy production in mitochondria, dopamine synthesis, thyroid function, and cell division. When reserves drop, these functions are affected first, while the bone marrow continues for a time to produce normal red blood cells. This explains very real symptoms despite perfect hemoglobin:
- Fatigue and endurance : a weariness that cannot be explained by sleep, a drop in training performance, shortness of breath climbing stairs.
- Head : declining concentration and memory, irritability, headaches, dizziness upon standing, feeling cold and cold extremities.
- Hair, nails, skin : diffuse hair loss, brittle or ridged nails, dull skin, paleness of the inner eyelids. See our article hair loss: 8 proven active ingredients.
- Legs : need to move legs in the evening or in bed (restless legs syndrome), associated with ferritin below 75 µg/L according to international guidelines.
- Immunity : recurrent ENT infections.
None of these signs is specific. Their accumulation in an at-risk person (menstruating woman, vegetarian, endurance athlete) justifies testing. The complete guide details the mechanisms.
4. Low ferritin, normal hemoglobin: why take action
Iron deficiency progresses in three stages: reserves become depleted (low ferritin, normal hemoglobin), then available iron is no longer sufficient for tissues (transferrin saturation coefficient below 20%), then the bone marrow produces smaller, less-loaded red blood cells (anemia). Standard blood count only detects the third stage. Someone with "normal blood work" often hasn't had ferritin measured.
In fatigued, non-anemic women (hemoglobin above 12 g/dL) but with ferritin below 50 µg/L, 12 weeks of iron reduced the fatigue score by 47.7%, compared to 28.8% with placebo. The authors recommend considering iron in fatigued women with low ferritin, with biological monitoring at six weeks.
Vaucher P, et al. CMAJ 2012;184(11):1247-1254. DOI: 10.1503/cmaj.110950
Two honest points: the placebo effect is real (nearly 30%), and iron did not improve overall quality of life or mood in this trial. It corrects iron-related fatigue. If fatigue persists with adequate ferritin, the investigation should be broadened (thyroid, vitamin D, B12, sleep); our guide chronic fatigue: 11 validated plants and nutrients covers all the angles.
5. "Normal" ferritin but deficient: the inflammation trap
Inflammation raiseshepcidin, the hormone that locks iron in storage cells. Paradoxical result: iron is present but inaccessible, tissues lack it, and blood ferritin rises because it is also an inflammation protein (Pasricha, Lancet, 2021). This is why guidelines for heart failure, chronic kidney disease, and inflammatory bowel diseases define deficiency as ferritin below 100 µg/L, or between 100 and 300 µg/L with a transferrin saturation coefficient below 20% (Cappellini, Am J Hematol, 2017).
Always request CRP along with ferritin. If it is elevated, ask for the transferrin saturation coefficient (TSC) : this is what indicates whether available iron is sufficient. And if you train hard, test at a distance from an intense session: exercise raises ferritin for 24 to 48 hours.
6. Causes of low ferritin
The body cannot eliminate iron; it only loses it through shed cells and blood. Low ferritin therefore means that losses or needs have exceeded absorption for months. The causes are detailed in the causes section of the complete guide ; the essentials come down to a decision tree:
7. How to raise your ferritin
A note on honesty regarding dose: at 18 mg, bisglycinate raises ferritin less than 60 mg of sulfate (Fischer, J Nutr, 2023), even though it is better absorbed per milligram. A nutritional dose is suitable for low reserves and maintenance; ferritin below 15 or anemia requires a corrective dose decided with your doctor. The complete comparison is in iron bisglycinate vs other forms of iron. On your plate, vitamin C from a acerola powder at meals doubles the absorption of plant-based iron, and vitamins B9 and B12 are iron's partners in making red blood cells.
The Bisglycinate Iron Nutrition•pro provides 14 mg of iron chelated with glycine (100% of NRV), 80 mg of vitamin C for absorption and 200 µg of vitamin B9. One vegetable capsule in the morning, with no metallic taste, made in France.
Discover Bisglycinate Iron →Not recommended in case of hemochromatosis, during pregnancy and breastfeeding without medical advice.
8. Low ferritin: when to consult without delay
You are a man or a postmenopausal woman with low ferritin: a digestive evaluation is recommended before any treatment (Pasricha, Lancet, 2021).
Hemoglobin is also low (less than 12 g/dL in women, 13 in men): this is anemia, which requires prescribed treatment and investigation of the cause.
You experience heart palpitations, shortness of breath at rest, or dizziness, black stools or blood in your stools: do not delay.
You are pregnant or breastfeeding : iron is often necessary, but the dose and form should be decided with your midwife or doctor.
Ferritin is not increasing after 3 months of taking iron properly: malabsorption or persistent losses to investigate.
Choose the line that matches your result: the answer will appear just below.
You are in the most common and most under-diagnosed case. Discuss it with your doctor with the exact figure: well-tolerated iron intake such as Bisglycinate Iron, in the morning on an empty stomach with vitamin C, for 3 months, then a follow-up test. Find the cause (menstruation, diet) so it doesn't happen again.
The Vaucher study showed benefit for fatigue up to 50 µg/L. Nutritional iron intake as bisglycinate iron for 3 months, vitamin C with meals and tea taken at a distance are often sufficient. For hair, aim for over 50 and allow 3 to 6 months for the hair growth cycle.
Ask for the transferrin saturation coefficient: below 20%, this is functional deficiency despite ferritin. In this case, oral iron is often poorly absorbed (elevated hepcidin) and management, sometimes by intravenous route, is the responsibility of the doctor monitoring your condition or training.
Ferritin below 15 or anemia: treatment prescribed at correction dose. Man or postmenopausal woman: screening for digestive bleeding and celiac disease testing before any supplementation. Iron will come after diagnosis, at the correct dose.
This test provides guidance; it does not replace professional medical advice.
Frequently asked questions about low ferritin
At what level is ferritin considered low?
Below 15 µg/L, reserves are depleted (WHO threshold). Below 30 µg/L, deficiency is very likely: at this threshold, ferritin detects 79% of deficiencies with 98% specificity according to the 2021 Cochrane review. In case of inflammation, 100 µg/L is used. With symptoms, many doctors aim for at least 50.
My ferritin is at 20 and the lab indicates "normal", is this a deficiency?
Probably. Laboratory reference ranges often start at 10 or 15 µg/L, values that correspond to an iron-depleted bone marrow. Studies show that average ferritin is 15 µg/L when reserves are zero and 70 µg/L when reserves are present. Ferritin at 20 with symptoms warrants discussion with your doctor.
What are the symptoms of low ferritin?
Persistent fatigue, reduced endurance, shortness of breath, concentration difficulties, feeling cold easily, hair loss, brittle nails, restless legs in the evening, pallor. These symptoms often appear while hemoglobin is still normal.
Can you have low ferritin without anemia?
Yes, this is the most common case. Ferritin drops first; hemoglobin only falls once reserves are depleted. A French trial showed that correcting ferritin below 50 µg/L reduced fatigue by 48% in non-anemic women (Vaucher, CMAJ, 2012).
Can normal ferritin hide an iron deficiency?
Yes. Ferritin rises with inflammation (infection, chronic disease, obesity, intense training). In case of elevated CRP, we rely on the transferrin saturation coefficient (below 20% = deficiency) and a ferritin threshold of 100 µg/L.
What are the causes of low ferritin?
Heavy periods, pregnancy, growth, endurance sports, diet poor in heme iron, malabsorption (celiac disease, antacids, bariatric surgery), blood donations and digestive losses. In men and postmenopausal women, low ferritin requires screening for bleeding.
How to raise ferritin quickly?
Treat the cause, choose a well-absorbed and tolerated form of iron (bisglycinate), take it in the morning on an empty stomach with vitamin C, every other day for high doses, away from tea, coffee and dairy products. Allow 3 to 6 months to rebuild reserves; in case of failure or malabsorption, your doctor may suggest intravenous iron.
How long does it take to raise low ferritin?
Fatigue improves in 4 to 6 weeks, hemoglobin normalizes in 4 to 8 weeks, but ferritin rises slowly: 3 to 6 months of supplementation are generally needed, with a follow-up check at 3 months.
What ferritin level should you aim for?
Minimum 30 µg/L, and above 50 µg/L in case of fatigue or hair loss. For restless leg syndrome, recommendations aim for above 75 µg/L. Beyond 300 µg/L in women or 400 in men without inflammation, this is considered excess.
Should you take iron as soon as ferritin is low?
In a menstruating woman or vegetarian with symptoms, iron supplementation is generally justified after medical consultation. In a man or postmenopausal woman, the cause must first be identified, particularly digestive bleeding, before correcting the level.
- Ferritin
- Protein that stores iron; its blood concentration reflects reserves, except in case of inflammation.
- CRP
- C-reactive protein, a marker of inflammation. Essential for interpreting ferritin.
- Transferrin saturation coefficient (TSI)
- Portion of the transport protein loaded with iron. Below 20%, tissues lack available iron.
- Hepcidin
- Liver hormone that blocks iron absorption and release when elevated (inflammation, recent iron intake).
- Iron deficiency anemia
- Final stage of deficiency: lowered hemoglobin, small and pale red blood cells.
- Garcia-Casal MN, Pasricha SR, Martinez RX, Lopez-Perez L, Peña-Rosas JP. Serum or plasma ferritin concentration as an index of iron deficiency and overload. Cochrane Database Syst Rev. 2021;5:CD011817. doi:10.1002/14651858.CD011817.pub2
- Garcia-Casal MN, Pasricha SR, Martinez RX, Lopez-Perez L, Peña-Rosas JP. Are current serum and plasma ferritin cut-offs for iron deficiency and overload accurate and reflecting iron status? A systematic review. Arch Med Res. 2018;49(6):405-417. doi:10.1016/j.arcmed.2018.12.005
- Pasricha SR, Tye-Din J, Muckenthaler MU, Swinkels DW. Iron deficiency. Lancet. 2021;397(10270):233-248. doi:10.1016/S0140-6736(20)32594-0
- Camaschella C. Iron deficiency. Blood. 2019;133(1):30-39. doi:10.1182/blood-2018-05-815944
- Vaucher P, Druais PL, Waldvogel S, Favrat B. Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ. 2012;184(11):1247-1254. doi:10.1503/cmaj.110950
- Cappellini MD, Comin-Colet J, de Francisco A, et al. Iron deficiency across chronic inflammatory conditions: international expert opinion on definition, diagnosis, and management. Am J Hematol. 2017;92(10):1068-1078. doi:10.1002/ajh.24820
- Stoffel NU, Cercamondi CI, Brittenham G, 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. Lancet Haematol. 2017;4(11):e524-e533. doi:10.1016/S2352-3026(17)30182-5
- Fischer JAJ, Pei LX, Elango R, et al. 18-mg ferrous bisglycinate vs 60-mg ferrous sulfate: a randomized controlled noninferiority trial. J Nutr. 2023;153(8):2453-2462. doi:10.1016/j.tjnut.2023.05.029
