Ferritin

Also known as iron stores

protein · no single molecular formula

LOINC 2276-4 code verified serum ng/mL

unverified These explanations are written to be easy to read and have not yet been checked against a source. The ranges and measurement notes on this page show theirs.

definition unverified

The protein your body stores iron in. The amount in your blood roughly mirrors how much iron you have in reserve.

Intracellular iron-storage protein; the small circulating fraction is proportional to total body iron stores under non-inflammatory conditions.

why measured unverified

It is the earliest sign that iron is running low, dropping well before anaemia shows up in a blood count.

No clinical version written yet.

if high unverified

Can mean too much stored iron, but far more often it just reflects inflammation somewhere, since this protein rises whenever the body is inflamed. That is why it is read alongside an inflammation marker.

No clinical version written yet.

if low unverified

Your iron reserves are running down. This is one of the few results where a low number means one clear thing. Common causes are blood loss, including heavy periods, not enough iron in the diet, or poor absorption.

Specific for depleted iron stores; no other common condition lowers it.

caveats unverified

Inflammation raises it independently of iron, so a normal result during an illness can hide a real shortage. If inflammation is present, the result cannot be taken at face value.

No clinical version written yet.

What this substance is

A 24-subunit protein shell that stores up to about 4500 iron atoms in its cavity. The assembly, not a single molecule, is what is measured.

UniProt P02794 · PDB 2FHA

Each molecule is drawn from ChEBI's curated 2D drawing, accepted only after its InChIKey, formula and charge matched the ChEBI release. Atom diagrams are checked against the NIST Atomic Spectra Database.

3D model

The ferritin shell: 24 heavy chains around a cavity that stores iron (PDB 2FHA; a recombinant protein, so a residue can differ from natural ferritin). Experimental structure from the Protein Data Bank, entry 2FHA, shown as its biological assembly (24 chains). Every chain was checked against its UniProt sequence (at least 99.4% identical). Drag to rotate, scroll to zoom.

Reference ranges

Checking your own result against this range needs the running application; this is a static copy. Nothing you type anywhere in Empeiria is ever sent to a server.

This open edition shows a range only where a public-domain or openly licensed source states one, and none does for this marker yet. Compare your result with the range printed on your own lab report.

How it is measured

In practice

A health worker takes a small blood sample from a vein in your arm with a needle. Your provider may ask you not to eat or drink for 12 hours first. The test is usually done in the morning.

Venous blood sample by venipuncture (serum ferritin). Patients may be asked to fast for 12 hours, and the test is usually performed in the morning.

Before the test

Fast (no food or drink) for 12 hours before the test if your provider asks.
Have the test in the morning if your provider advises.

Where: laboratory

Source: Ferritin Blood Test, MedlinePlus (U.S. National Library of Medicine) cited · not yet checked by a person

In the lab

immunoassay

Chemiluminescent sandwich immunoassay

Two antibodies grab onto the protein together, and one of them carries a tag that gives off light. More light means more ferritin.

Two ferritin-specific antibodies, one of them labelled, bind ferritin to form a sandwich that is captured on a solid phase; the light signal is read against a calibration curve.

What can throw it off

High-dose biotin supplements (over 5 mg a day) can interfere with assays that use a biotin-streptavidin capture step; samples should be taken at least 8 hours after the last dose.

Why labs disagree: Immunoassays from different manufacturers use different antibodies, and results can differ a lot for the same sample: in one comparison of two common analysers, one read 36-44% higher than the other. Ferritin results are therefore best compared on the same assay, and a lab's range applies to its own method.

Sources: Comparison of two ferritin assay platforms to assess their level of agreement in measuring serum and plasma ferritin levels in patients with CKD (BMC Nephrol 2023), PMC open access; NHANES 2017-2018 Laboratory Procedure Manual: Ferritin (Roche cobas e601), CDC/NCHS cited · not yet checked by a person

What it reports on

liver stored by
The liver is the body's main iron store, and it keeps that iron inside ferritin.
spleen stored by
The spleen holds iron-storing ferritin and recycles iron from old red blood cells.
bone marrow stored by
Bone marrow macrophages store iron, and low blood ferritin tracks with low marrow iron.

Associated symptoms

When high

high Joint pain · suggestive · occasional
Iron overload deposits in joints, classically the knuckles.

When low

low Feeling tired all the time · non specific · common
Iron is required for oxygen transport and for cellular energy production.
low Looking unusually pale · suggestive · occasional
low Hair thinning or falling out · suggestive · occasional
Hair follicles are among the first tissues affected by low iron.
low Getting out of breath easily · suggestive · occasional
low Spoon-shaped nails · characteristic · rare
Long-standing iron deficiency; uncommon, but points strongly at it when present.
low Trouble thinking clearly · non specific · occasional

Conditions this marker features in

When high

high Iron overload · defining
The clinical diagnosis rests on showing raised iron stores with a high ferritin, together with the gene result. Ferritin is also followed during treatment.
high Anaemia caused by long-term illness · supportive
Ferritin is normal or raised (often above 100 µg/L), unlike iron deficiency where it is low (below 30 µg/L). It is the most useful test for telling the two apart.
high Anaemia from red cells breaking down too fast · supportive
Ferritin can be high when red cell breakdown has gone on for a long time.

When low

low Low iron causing anaemia · defining
The key test for confirming iron deficiency. Below 15 µg/L means iron stores are empty, and is almost never seen without iron deficiency. Inflammation can make ferritin look normal.
low Low white blood cell count · supportive
Iron deficiency was the most common cause found in one study of isolated leukopenia. Ferritin was part of the workup.

Either direction

either Carrier of beta-thalassaemia · supportive
Checked to tell the trait apart from iron deficiency, which also gives small red cells. Ferritin is usually normal in the trait; a low ferritin points to iron deficiency, which can also be present at the same time.

Ordered as part of

iron_studies · vitamins