Ferritin test: what it measures, normal levels, and what low or high ferritin means

Ferritin is a hollow protein shell that packs away iron inside cells — mostly in the liver, spleen, bone marrow and muscle — so it can be released when the body needs to make hemoglobin. A small amount leaks into the blood in proportion to those stores, and that is what the serum ferritin test measures, in nanograms per milliliter (ng/mL, identical to µg/L).

Because it tracks the reserve rather than the iron currently in transit, ferritin is more informative than a serum iron level, which swings with meals and time of day. It is also the earliest marker to fall: stores drain first, then the iron available for red-cell production drops, and only then do hemoglobin and red-cell size fall enough to be called anemia. A low ferritin with a normal hemoglobin is iron deficiency without anemia — common, symptomatic and worth finding.

Ferritin has one important complication: it is also an acute-phase reactant, meaning the liver releases more of it during infection, inflammation, liver injury and some cancers regardless of iron stores. That is why it is often read with CRP and transferrin saturation rather than alone.

Ferritin is the storage form of iron, so low ferritin means the stores are running down even while hemoglobin is still normal — and that stage can already produce symptoms:

High ferritin is more often a sign of inflammation, liver disease, heavy alcohol use, metabolic syndrome or a recent infection than of true iron overload — ferritin is an acute-phase protein that rises whenever the body is inflamed. Genuine overload (hemochromatosis) brings joint pain, fatigue and abdominal pain and, over years, liver, heart and endocrine damage; a transferrin saturation above about 45% is the clue that iron itself is high.

Low ferritin almost always has a cause worth finding — heavy periods, low dietary intake, celiac disease or other malabsorption, or blood loss from the gut — so a low result is a reason to look for the source as well as to replete.

Ferritin is the test for anyone with symptoms of low iron: persistent fatigue, exercise intolerance, shortness of breath on exertion, brain fog, headaches, restless legs, hair shedding, brittle nails, cold hands and feet, cravings for ice or non-food items, and a sore or smooth tongue. It is the natural follow-up to a complete blood count showing small (low MCV) or pale red cells, or a hemoglobin in the low-normal range.

Certain groups lose or under-absorb iron and are tested more readily: menstruating women, especially with heavy periods; pregnant women and women planning pregnancy; endurance athletes; vegetarians and vegans; frequent blood donors; people with celiac disease, inflammatory bowel disease, previous gastric surgery or long-term acid-suppressing medication; and anyone with gastrointestinal bleeding, including men and postmenopausal women in whom iron deficiency itself is a reason to look for a source.

At the other end, ferritin is checked when iron overload is a possibility: a family history of hereditary hemochromatosis, unexplained liver enzyme elevation, joint pain with fatigue in middle age, or as part of monitoring after repeated transfusions. It also tracks the response to iron treatment.

Ferritin is a standard blood draw with no fasting requirement of its own; if it is bundled with serum iron and transferrin saturation, a morning fasting draw makes those companion values more reliable. Taking an iron supplement the day of the test spikes serum iron but changes ferritin very little, so there is no need to stop iron for the test itself — just tell whoever interprets the result that you are taking it.

Timing around illness matters more than timing around meals. Because ferritin rises with inflammation, a draw during or in the two to three weeks after an infection, flare or injury can read falsely reassuring. If you have been sick, wait until you have recovered, or ask for a CRP alongside so the reader can see whether inflammation is present.

You can order ferritin on its own or inside an iron or anemia panel online through TestWell; a physician reviews the order, you visit a nearby Quest or Labcorp patient service center, and results appear in your portal within a few business days.

The reference ranges printed on lab reports are wide — around 24 to 336 ng/mL for adult men and 11 to 307 ng/mL for adult women in the range TestWell's catalog uses — because they describe the spread in the general population, which includes many people with unrecognized iron deficiency and many with mild inflammation. They are not the same as the level at which iron stores are adequate.

For diagnosis, guidelines draw the line higher than the bottom of the lab range. The British Society of Gastroenterology's 2021 guideline treats a ferritin below 30 ng/mL as diagnostic of iron deficiency in adults, with a specificity above 90%; the World Health Organization uses below 15 ng/mL as the threshold for depleted stores in healthy adults and below 70 ng/mL in people with infection or inflammation. In practice a ferritin between 15 and 30 ng/mL in a woman is 'within range' on the report and still indicates empty stores. Some clinicians aim higher for specific problems such as restless legs or hair shedding, though the evidence for those targets is weaker.

Any process that activates the immune system — a cold, a dental infection, an autoimmune flare, obesity's low-grade inflammation, chronic kidney disease, heart failure or cancer — raises ferritin independently of iron. In these settings a person with genuinely empty stores can have a ferritin of 60, 80 or more. A CRP drawn at the same time reveals whether inflammation is present, and transferrin saturation (serum iron divided by total iron-binding capacity) helps because it falls in true deficiency; a saturation under about 20% with a 'normal' ferritin and a raised CRP is a common picture of hidden iron deficiency.

This is why ferritin is interpreted as part of an iron panel rather than as a stand-alone number in anyone who is unwell, and why the WHO applies a much higher cut-off in the presence of inflammation.

Most high ferritin results are not iron overload. In order of how often they turn up, the usual explanations are inflammation or infection, fatty liver disease and the metabolic syndrome, regular alcohol use, other liver injury, and then true iron overload from hereditary hemochromatosis, repeated transfusions or long-term iron therapy. Very high values — in the thousands — appear with severe infection, some blood cancers, hemophagocytic syndromes and adult-onset Still's disease.

The test that separates overload from the rest is transferrin saturation: a saturation above 45% alongside a raised ferritin points toward iron loading and usually leads to HFE gene testing for hemochromatosis. A high ferritin with a normal saturation is far more often metabolic or inflammatory, and improves when the underlying cause is addressed. The high-ferritin section below lists the causes, symptoms and follow-up tests in more detail.

A low ferritin confirms iron deficiency; the next question is why. In menstruating women heavy periods are the usual answer, but guidelines advise that men and postmenopausal women with iron deficiency have their gastrointestinal tract evaluated for a source of blood loss, and that celiac disease be tested for in everyone, because it is a common silent cause of poor absorption. A complete blood count shows whether anemia has developed, and the form and route of iron replacement are decided with a clinician based on severity, tolerance and cause.

Ferritin refills slowly: hemoglobin improves within weeks of effective treatment, but ferritin needs roughly three months of consistent iron before a recheck can confirm stores have recovered. A high ferritin is followed with CRP, liver enzymes, a metabolic check and transferrin saturation, with genetic testing and imaging reserved for the overload pattern.