Ferritin: what the blood test shows about your iron
Ferritin is the blood test for your iron stores, and a result under 30 ng/mL in the reproductive years and perimenopause, or under 30 µg/L in puberty, means low stores. A low ferritin level is raised with prescribed iron after a blood test, together with treating whatever is draining the iron, such as heavy periods, and the test sits among the health checks for women as a pair with a blood count.
Low iron stores are common, and they are treatable, so a low result is information to work with and not a verdict. Think of ferritin as a gauge for the iron your body holds in reserve, and a simple one to ask about. This page covers who tends to run low and why, when a test is worth asking for, what raising it involves, and how far the research goes.
What is ferritin?
A ferritin blood test is the check used to judge iron stores, and a lab report may call it serum ferritin, ferritin level or ferritin count. All three mean the same test. The World Health Organization's 2020 guideline uses ferritin in two ways: to assess iron status, and to monitor how iron treatment is working. So the test that finds low stores is also the one that shows them recovering.
Ferritin is usually ordered with a blood count: a complete blood count (CBC) in the US, and a full blood count (FBC) in the UK. Ferritin speaks to iron stores, while the blood count is where anemia (anaemia in the UK) shows up. Iron deficiency and iron-deficiency anemia are two separate things, which is why the two results are read side by side.
What does the evidence say about low ferritin?
If you or your daughter are running low, you are in very large company. Iron stores tend to dip when the body is losing blood, growing fast or both, and each stage has its own reason, which is worth looking for.
In puberty, periods begin and growth speeds up. Blood loss from periods plus rapid growth raises iron needs, so iron deficiency is common, and the tiredness and poor concentration it causes are often the first things a teenager or her parent notices (NIH Office of Dietary Supplements).
In the reproductive years, iron deficiency is the most common nutrient deficiency in women, mostly from periods and pregnancy (NIH Office of Dietary Supplements). In the UK, the NHS likewise names heavy periods and pregnancy as very common causes of iron deficiency anaemia.
In perimenopause, heavy or irregular bleeding can drain iron stores, so bleeding that has changed is worth mentioning when ferritin comes up.
Weyand and colleagues, in a 2023 JAMA research letter, looked at nonpregnant US females aged 12 to 21 and found iron deficiency (ferritin under 25 µg/L) in about 38.6%, and iron-deficiency anemia in about 6.3%. Most iron deficiency therefore occurs without anemia, so a normal blood count does not rule out low stores.
Girls who had not yet started their periods had low ferritin too: 27.1% were iron deficient at that cutoff, which points to causes other than menstrual loss.
When a result does come back low, our page on iron deficiency anemia treatment goes through what usually follows.
How low is low, and how often is ferritin tested?
The low-stores line is 30 at each stage that has one. The puberty guidance writes it in µg/L and the adult stages in ng/mL; the two units are equivalent, so the number reads the same on either report.
How often is simpler than it sounds: there is no calendar for ferritin. The guidance ties the test to what is happening in your body. Heavy periods and frequent tiredness are the prompts from puberty through perimenopause, and planning a pregnancy is a further one in the reproductive years. It sets no routine repeat beyond those prompts.
Once iron has been prescribed, the timing of the next blood test is set by the prescriber, not by a fixed interval in the guidance, so it is worth asking at the first appointment when your ferritin will be checked again.
Iron comes after the test, not before it. From puberty through perimenopause, the guidance is iron only when ferritin is low, as prescribed, because too much iron is harmful (NIH Office of Dietary Supplements). Our guide to iron supplements for women covers how that tends to work.
In the UK, the NHS page on iron deficiency anaemia describes the FBC as the usual test and does not mention ferritin, so a GP may begin there, and it is reasonable to ask whether ferritin can be added.
What did the studies show and not show?
The Weyand letter drew on US national survey data from 2003 to 2020. It counts how many had low ferritin. It does not show why any one person's stores are low, and it does not cover pregnancy, the later reproductive years or perimenopause.
It also showed how much the answer depends on where the line is drawn. At under 15 µg/L, 17% counted as iron deficient; at under 50 µg/L, 77.5% did, in the same group and the same samples.
None of its cutoffs was 30, so its percentages sit beside the under-30 line used in the guidance and do not test it directly.
The figure for girls before their first period is an estimate with a wide margin: a 95% confidence interval of 17.1% to 37.0%. It shows that low ferritin happens before periods begin, not what causes it.
Ferritin and iron tests by life stage
| Stage | Figure | Why | Read more |
|---|---|---|---|
| Childhood | No low-stores line set | The under-30 line begins with the puberty guidance, when periods and rapid growth raise iron needs; the childhood page lists the checks named for younger girls. | Health checks |
| Puberty | Under 30 µg/L | Periods and rapid growth raise iron needs; check if periods are heavy or she is often tired. | Health checks |
| Reproductive years | Under 30 ng/mL | Check if periods are heavy, you are tired or you are planning pregnancy. | Health checks |
| Perimenopause | Under 30 ng/mL | Heavy or irregular bleeding can drain iron stores. | Health checks |
| Menopause | No low-stores line set | The guidance ties ferritin testing to heavy periods and pregnancy planning in the earlier stages and sets no line for this one; the menopause page lists the checks that are named. | Health checks |
| Postmenopause | No low-stores line set | With periods over, the bleeding that prompts a ferritin check in earlier stages no longer applies, and the guidance gives no line here; the postmenopause page lists the checks that are named. | Health checks |
Facts
Common questions
How to increase ferritin levels?
Ferritin rises when low stores are treated with prescribed iron, so the first step is the right appointment. In the US, a primary care provider or OB-GYN can order the test, and a pediatrician can for a teenager. In the UK, a GP is the person to ask. A good opening question is whether ferritin can be checked with a blood count.
How to raise ferritin levels?
When iron is prescribed for low ferritin, the schedule is worth a question. The guidance for puberty (NIH Office of Dietary Supplements) notes that taking iron every other day can improve absorption and reduce stomach upset. Whether an alternate-day schedule suits you or your teenager is for the prescriber to say, since the dose is set after a blood test.
How to boost ferritin levels?
A lasting boost usually means dealing with where the iron is going as well as putting iron back. For the reproductive years, the guidance (NIH Office of Dietary Supplements) is to check ferritin and treat heavy periods together. If your periods are heavy, it is worth asking your OB-GYN, or your GP in the UK, about treatment for the bleeding itself.
How to improve ferritin levels?
Improving ferritin takes months, so patience is normal. In the UK, the NHS says iron tablets for iron deficiency anaemia are usually taken for about six months, with or soon after food. If you have been prescribed iron in the US, it is worth asking at the start how long your own course is expected to run.
How to increase ferritin?
The evidence supports adding iron only when a blood test shows ferritin is low. Mentioning heavy periods, pregnancy plans or how long you have felt tired helps your doctor decide on the test. If your result is not low, iron is not what the guidance offers; a good next question for the same doctor is what else could explain the tiredness and whether other checks would help.
Next steps
A gentle place to start is with your own notes: how many days your periods last, how your energy has been, and whether pregnancy is on your mind. From there, you might ask whether a ferritin test and a blood count would be useful, and, if a result comes back low, what the likely reason is and whether iron makes sense for you. For a teenager, the same conversation can happen with a parent alongside. If tiredness or other symptoms keep getting worse, or you are losing weight without trying to, that is worth a doctor's visit sooner, so the cause can be found instead of wondered about. Your stage of life, your history and your own preferences all shape what happens next, and you are the one who decides what fits, because this is not one size fits all.
See a doctor promptly if you have
- Unexplained weight loss
- Symptoms that are getting worse
Sources
The guidelines and studies this page draws on.
- Prevalence of Iron Deficiency and Iron-Deficiency Anemia in US Females Aged 12-21 Years, 2003-2020 (Weyand et al., JAMA research letter), JAMA / PubMed Central (2023)
- WHO guideline on use of ferritin concentrations to assess iron status in individuals and populations, World Health Organization (2020)
- Iron deficiency anaemia, NHS (undated)
- NIH Office of Dietary Supplements: calcium, iron and vitamin D intakes, National Institutes of Health (undated)
- NIH Office of Dietary Supplements: iron, calcium, iodine and vitamin D intakes, National Institutes of Health (undated)
- NIH Office of Dietary Supplements: calcium, vitamin D and iron intakes, National Institutes of Health (undated)