What is ferritin? What a ferritin blood test measures

Ferritin is a protein that stores iron inside cells. A small amount also circulates in the blood, and a ferritin blood test measures that amount. Doctors use it as an indicator of how much iron the body has in reserve.

Why a ferritin test is ordered

MedlinePlus lists several reasons. Ferritin is often one of a set of iron tests, used to help diagnose or rule out iron deficiency anaemia (anemia in US spelling), too much iron in the body (haemochromatosis) and some other conditions. It is also used to monitor some long-term illnesses, to screen people who are at higher risk of iron deficiency, and to check whether iron treatment is working.

What the test involves

A health professional takes a small blood sample from a vein, usually in the arm. It takes a few minutes. Depending on the laboratory and the other tests being run, you may be asked to fast beforehand, and the sample is often taken in the morning. Check the instructions you are given, because they differ.

What a result can reflect, in general

In general terms, MedlinePlus says a low ferritin may point to iron deficiency anaemia or another condition linked to low iron. A high ferritin most often reflects extra iron in the body, but it can also be raised by inflammation, including infection or surgery, and by liver disease, some autoimmune conditions, obesity, alcohol use disorder and an overactive thyroid. Some medicines can raise or lower it as well.

That is why a ferritin result is read alongside other tests, symptoms and medical history, and why an unusual number does not by itself mean a condition that needs treatment. Interpreting your own result is a conversation for your doctor.

The unit and the laboratory matter

Ferritin is printed as ng/mL on many United States reports and as µg/L on many in the UK and Australia (the two are the same quantity), and a few laboratories use pmol/L. Each laboratory also publishes its own reference range, written in its own unit. Write the unit down next to the number every time, and take the range from the report you were given rather than from another country’s.