Ferritin test: what the ranges mean

This page explains the test and what official guidance says. It is not medical advice, and it cannot tell you what your own result means. A clinician orders the test, reads it with your other results, and looks for the cause of a low number.

What a ferritin test measures

Ferritin is the protein your body uses to store iron. A blood test for ferritin shows how full those stores are. The NIH calls it “the most efficient and cost-effective test for diagnosing iron deficiency.”

It catches low iron early. Stores run down first, and hemoglobin, the anemia number on a blood count, falls only once they are used up. So ferritin can be low while your blood count still looks normal.

What the ranges mean

Results are given in ng/mL, which is the same as mcg/L. Each lab prints its own normal range, and many start somewhere from 15 to 30, so a result in the 20s can be flagged normal.

• Under 10: the NIH says this “suggests” iron-deficiency anemia.
• Under 15: used-up iron stores in adults, the line the World Health Organization uses (WHO 2020; Daru 2017). It is also the line in our CDC analysis below.
• Under 30: “suggests iron deficiency” (NIH). The British Society of Gastroenterology uses the same line (BSG 2021).
• High: ferritin over 200 in women or 300 in men was the line for high iron stores in a large study of older adults that the NIH cites. High ferritin has many causes, including inflammation and iron overload, and needs a clinician to sort out.

What can throw the number off

Inflammation raises ferritin without adding any iron. An infection, a flare-up of a long-term illness or liver disease can do it. Across 32 studies, inflammation raised ferritin by about 30% (Thurnham 2010). That is why a clinician may order a CRP test, a marker of inflammation, with it. If CRP is high, a “normal” ferritin does not rule out low iron.

Who tends to be low

Low ferritin is common in women of childbearing age and rare in men. Monthly blood loss is the main reason. Pregnancy, blood donation, vegetarian diets, gut bleeding, celiac disease and weight-loss surgery also lower iron. See the risk list on our deficiency page.

Low iron in a man, or in a woman past menopause, needs a doctor. Without monthly blood loss, the cause is often bleeding somewhere, most often in the gut, and guidelines advise looking for it (BSG 2021; Ko 2020).

Before you take iron

• Test first. The body has no good way to get rid of extra iron, so it can build up. The upper limit for adults is 45 mg a day from food and supplements (NIH).
• People with hereditary hemochromatosis, a genetic condition that makes the body absorb too much iron from food, have a higher risk of iron overload (NIH). Talk to a doctor before taking any iron.
• Keep iron away from children. The FDA requires iron pills to carry this warning: “Accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6.”

After starting iron

Hemoglobin usually starts to rise within about 2 weeks. Ferritin, the stores, refills much more slowly. Guidelines advise keeping going for about 3 months after hemoglobin is back to normal, to refill the stores (BSG 2021). Your clinician sets the dose and when to recheck. Ask that the recheck includes ferritin, not just a blood count.

Questions to ask your clinician

• What was my ferritin, and what range does this lab use?
• Was CRP or another inflammation test done with it?
• If I am low, what is the likely cause, and does it need looking into?
• If I should take iron, how much, how often, and when do we recheck ferritin?

If your clinician recommends iron, our iron supplement guide compares the forms and what they cost. The iron dosage guide covers how much and how often.