Ferritin, iron and CRP: why a normal ferritin can be misleading
Short answer: ferritin shows how much iron your body has stored, but it also rises when you have inflammation. A result that looks normal can therefore hide low iron stores if you also have an infection or inflammation, which is why ferritin is often read alongside CRP.
What ferritin measures
Ferritin is a protein that stores iron inside your cells. A small amount circulates in the blood, and that amount normally reflects your stores. A low result on a ferritin blood test is a reliable sign of low iron stores. A normal or high result is less clear-cut.
Why inflammation can mask low iron
Doctors call ferritin an acute-phase protein: it goes up during infection and inflammation, with some liver conditions and with heavy alcohol use. If your body is inflamed, ferritin can look reassuring even though your stores are low.
Where CRP fits in
CRP (C-reactive protein) is a marker of inflammation. The high-sensitivity CRP test can pick up low-level inflammation that a standard CRP might miss. If CRP is raised, a ferritin result needs more cautious reading, and a clinician may also look at transferrin saturation and a full blood count. The iron status profile brings several of these markers together.
Who may want to check their iron stores
People with heavy periods
Vegetarians and vegans
Regular blood donors
Endurance athletes
People with ongoing fatigue, hair thinning or breathlessness on exertion (these have many possible causes, so a test is a starting point rather than an answer)
People with a condition that affects absorption, such as coeliac disease
Do not start high-dose iron without a result
Iron supplements commonly cause stomach upset and constipation, and too much iron is harmful for people who absorb it excessively, such as those with haemochromatosis. A blood test first tells you whether iron is the problem at all.
Frequently asked questions
What is a normal ferritin level?
It depends on the laboratory, your age and sex, and your wider health. Values below roughly 15 to 30 micrograms per litre are commonly taken to suggest low iron stores, but use the range printed on your own report and ask a clinician to interpret it.
Can ferritin be high without too much iron?
Yes. Inflammation, liver conditions, heavy alcohol use and metabolic problems can all raise ferritin without the body holding extra iron. A clinician may check transferrin saturation to tell the difference.
Should I take iron if my ferritin is low?
Speak to a clinician first. Low iron stores have a cause, such as heavy periods, diet, absorption problems or bleeding, and in men and women after the menopause a clinician will usually want to rule out blood loss before simply treating the number.
Do I need to fast for a ferritin test?
Usually not, but check the preparation notes on the test page. If you also have serum iron measured, a morning sample is often preferred.
See a doctor promptly if you notice black or bloody stools, very heavy bleeding, chest pain or marked breathlessness.
Related reading
Clinically reviewed by Zak Toon, ACP, on 15 October 2026.
This article is general information based on UK guidance from NHS and NICE. It is not personal medical advice. If you are worried about your health or have symptoms, speak to your GP or call 111.
