Ferritin reflects the amount of iron stored in your body (your iron stores). When iron runs short, these stores are the first to drop, and hemoglobin falls only after that. So ferritin alone can be low while hemoglobin is still within the reference range, a state that’s sometimes called “hidden anemia.” Ferritin also reads high when there’s inflammation, so whether it’s low or high, it’s important to read it together with other markers.
What ferritin reflects
Besides carrying oxygen as a building block of hemoglobin, iron is involved in the enzymes that make energy in the mitochondria, and in the enzymes that make neurotransmitters such as dopamine, serotonin, and noradrenaline.
About two-thirds of the iron in your body is in hemoglobin, and much of the rest is stored in the liver, spleen, and bone marrow, in forms such as ferritin. Serum ferritin tracks closely with the size of these stores, so it gives you a clue to how much iron your body has in reserve. It’s measured in ng/mL (the same number as μg/L).
The body has almost no way of actively getting rid of iron, so it keeps its iron level steady by adjusting how much it absorbs from the gut.
Main iron-related markers
These are the main markers to read alongside ferritin. The reference ranges are Japan’s shared reference intervals (JCCLS).
| Marker | What it reflects | Shared reference interval (JCCLS) | Precision nutrition optimal range |
|---|---|---|---|
| Hemoglobin (Hb) | The amount of the protein inside red blood cells that carries oxygen | Men 13.7–16.8 g/dL, women 11.6–14.8 g/dL | Women 13–14 g/dL, men 14–15 g/dL |
| MCV | The average size of a single red blood cell | 83.6–98.2 fL | Women 88–92 fL, men 90–93 fL |
| Serum iron (Fe) | The amount of iron being carried in the blood | 40–188 μg/dL | Women 60–100 μg/dL, men 100–120 μg/dL |
| CRP | A clue to inflammation in the body | 0.00–0.14 mg/dL | 0–0.05 mg/dL |
| Ferritin | The amount of iron in storage | Not included in the shared reference intervals | Women 50–80 ng/mL, men 100–150 ng/mL |
The right-hand column shows the precision nutrition optimal ranges I use in my counseling. These are precision nutrition guides, not medical reference ranges. Falling outside them doesn’t by itself mean you have too much or too little iron, or that you have an illness.
The shared reference intervals are the ranges that hold the middle 95% of values measured in healthy people; they aren’t meant to decide whether you’re ill. Reference ranges for ferritin are set for each lab or measurement method, and they’re usually given separately for men and women. At some facilities the lower limit is quite low, so even a result “within the reference range” doesn’t necessarily mean your stores have room to spare.
If your results include TIBC (total iron-binding capacity: the sum of serum iron and a marker called UIBC), you can work out “serum iron ÷ TIBC × 100” to find the share of the iron-carrying protein that’s bound to iron (transferrin saturation).
What low ferritin can mean
Ferritin drops before hemoglobin does
A shortage of iron is thought to develop in stages. First, stored iron decreases and ferritin falls. Next, the iron carried in the blood (serum iron and transferrin saturation) decreases. If the shortage progresses further, the body can no longer make enough red blood cells: hemoglobin falls, and red blood cells become smaller (a drop in MCV).
“Hidden anemia” isn’t a medical term, but it’s close to what medicine calls “latent iron deficiency” or “iron deficiency without anemia”: a stage before anemia in which the stores have already dropped. In a trial of menstruating women who had low ferritin but no anemia, a link was reported between a shortage of iron and getting tired easily.
What counts as “low”
Thresholds for ferritin differ depending on who sets them. The 2020 guideline from the World Health Organization (WHO) uses ferritin below 15 ng/mL as the threshold for iron deficiency in healthy adults. The guideline the American Society of Hematology (ASH) published in 2026 sets the threshold for adults without inflammation higher than WHO does, at 30 ng/mL or below, and says there’s room to consider a threshold of 50 ng/mL or below for people who are feeling off, or whose circumstances make them more likely to run short on iron (though the evidence for this is described as still insufficient).
People and situations where it tends to run low
- People who menstruate, especially those with heavy periods
- People who are pregnant or have recently given birth, and children who are still growing
- People who eat small amounts, or who eat little meat or fish
- People who do endurance exercise such as long-distance running, and people who donate blood often
- People with low stomach acid (for example, from atrophic gastritis, an H. pylori infection, or long-term use of medication that reduces stomach acid), people who’ve had stomach surgery, and people with inflammation in the gut
- People who keep taking painkillers (NSAIDs), or medications that make the blood less likely to clot, such as low-dose aspirin
If your periods feel heavy, talking with a gynecologist may help find the cause. When iron deficiency anemia is found in a man or in a woman after menopause, it’s recommended to check whether something such as bleeding from the digestive tract is behind it. If you find out you’re low on iron, even without anemia, please talk with a doctor about it.
What high ferritin can mean
It reads high when there’s inflammation
Ferritin is also one of the “acute-phase proteins,” which increase when there’s inflammation in the body. During an infection, with inflammation in the joints or gut, after an injury, and in similar situations, ferritin goes up regardless of how much iron is stored.
When there’s inflammation, the liver makes more of a hormone called hepcidin, which holds back both the absorption of iron from the gut and the release of stored iron into the blood. That makes a combination of high ferritin and low serum iron more likely, and even when iron is actually running short, ferritin can appear to be within or above the reference range. The WHO guideline uses ferritin below 70 ng/mL as a clue to iron deficiency in adults with an infection or inflammation, and the ASH guideline uses ferritin below 100 ng/mL or transferrin saturation below 20% as a clue in adults with anemia of inflammation.
Reasons other than inflammation
- Strain on the liver: When liver cells are damaged, for example by fatty liver or drinking too much alcohol, ferritin is released into the blood. It’s read together with GGT (γ-GTP), AST, and ALT. There are also reports linking it to metabolic imbalances such as excess weight and high blood glucose.
- Too much iron: This includes hereditary hemochromatosis (uncommon in Japan) and repeated blood transfusions. It has also been pointed out that iron may build up in people who keep taking fairly large amounts of iron supplements for a long time. A typical feature is that transferrin saturation is high as well.
- Other causes: It can also run high with illnesses other than inflammation, such as cancer or kidney disease.
For healthy adults, the WHO guideline takes values above 150 ng/mL in menstruating women, and above 200 ng/mL in men and in women who don’t menstruate, as a clue that there may be too much iron, while adding that this shouldn’t be judged from ferritin alone. If your values stay high, please have a doctor look into the cause.
How I read the numbers
Where you sit within the reference range
What follows isn’t a medical standard. It’s the way I read blood data, from a precision nutrition perspective. I look not only at whether a value falls within the reference range, but also at which side of the range it leans toward. For the iron-related markers, I compare values with the precision nutrition optimal ranges in the right-hand column of the table above.
For ferritin, whether it falls below the bottom of the optimal range is one of the clues I use to think about how much iron you have in reserve. The 50 ng/mL for women lines up with the value the ASH guideline gives for people such as those who are feeling off. The 100 ng/mL for men isn’t a number the guidelines give for adults without inflammation. Men don’t lose iron through menstruation and usually have larger stores than women, so their optimal range is higher than women’s, too. The optimal range for women isn’t split into before and after menopause. Falling below the bottom of the optimal range doesn’t by itself mean you’re short on iron, and it doesn’t mean you need a supplement. And higher isn’t always better.
When CRP is above its optimal range, I also consider the possibility that ferritin is reading high because of inflammation.
Reading it alongside other markers
- Ferritin on the low side, MCV in the middle of the reference range: A combination often seen at a stage when only the stores have dropped and red blood cells haven’t been affected yet.
- Ferritin on the low side, with hemoglobin and MCV also leaning toward the low end of the reference range: I consider the possibility that the iron shortage is starting to affect red blood cell production.
- Ferritin on the low side, but MCV in the upper part of the reference range or above it: Factors that make red blood cells larger, such as a shortage of vitamin B12 or folate, how much you drink, low thyroid function, or the state of your liver, may be overlapping and making the iron shortage harder to see.
- Ferritin on the high side, CRP also high, and serum iron low: I consider the possibility that inflammation is making iron harder for the body to use, and I don’t judge the size of your stores from that ferritin result.
- Ferritin on the high side, and liver markers also high: I consider the possibility that strain on the liver is involved.
- Only serum iron is high or low: Serum iron changes even over the course of a day, and it can read high right after a meal or a supplement, or because of hemolysis during the blood draw, so I don’t judge from a single value. Transferrin saturation swings in the same way, so if possible, I look at blood drawn in the morning on an empty stomach, before taking any iron supplement.
Watch the change, not a single result
Ferritin as a measure of your stores moves slowly, over weeks to months, but with inflammation it can rise within a few days. So it’s best to avoid testing at times such as right after a cold or the day after intense exercise and, ideally, to test with the same lab under the same circumstances. I then follow how the value has changed since last time.
What you can revisit in everyday life
How you get iron from food
The iron in food comes in two forms: “heme iron,” plentiful in meat and fish, and “non-heme iron,” plentiful in soy foods, leafy greens, seaweed, and the like. Heme iron is absorbed more easily, while non-heme iron is more easily affected by what you eat with it.
- Things that tend to help your body absorb non-heme iron: vitamin C, and meat and fish (this isn’t an effect of protein in general)
- Things that tend to lower absorption: polyphenols such as the tannins in green tea, black tea, and coffee; calcium; phytic acid in grains and beans; soy protein; and eggs
How you combine foods changes how much iron you absorb from a single meal: for example, not drinking tea or coffee right before or right after a meal, and pairing leafy greens and soy foods with meat or fish, or with vegetables and fruit. However, across your usual diet as a whole, the difference is said to be smaller than when a single meal is studied. Your stores are thought to depend more on how much iron-containing food you eat, and on how much iron you lose through menstruation and the like, than on how you combine foods.
The Dietary Reference Intakes for Japanese (2025 edition) from Japan’s Ministry of Health, Labour and Welfare set the recommended amount of iron for ages 18 to 64 at 7.0–7.5 mg a day for men, 6.0 mg for women who don’t menstruate, and 10.0–10.5 mg for women who do.
Before you use a supplement
In healthy people, absorption from the gut is regulated, so getting too much iron from food is very unlikely. But because the body has almost no way of getting rid of iron, it’s said that if you keep taking supplements in amounts well above the recommended amount for a long time, the possibility of iron building up in the organs can’t be ruled out. The Dietary Reference Intakes also say that intake well above the recommended amount should be avoided, except in cases such as when a doctor gives iron for anemia. It’s reassuring to decide whether to use one, and how long to keep it up, by talking with a doctor or pharmacist while measuring ferritin and other markers. If you’ve been prescribed iron medication, please follow your doctor’s instructions first.
If you’re concerned
In cases like these, please talk with a doctor:
- Your hemoglobin or ferritin is below the reference range printed on your results, or your ferritin has dropped sharply since last time
- You keep having shortness of breath, a racing or pounding heart, or dizziness when you stand up
- Your periods are heavy or last a long time
- Your stools are black, or you’re losing weight for no clear reason
- You’re a man, or a woman past menopause, and you’ve been found to be low on iron
- Your ferritin stays high
Even if you think a medication you usually take, such as one that reduces stomach acid or one that makes the blood less likely to clot, might be involved, please don’t stop it on your own; talk with your doctor.