FER (Ferritin)

Ferritin is a protein that stores iron in the body, and measuring its level in the blood is the best single indicator of how much iron you have in reserve. Because it reflects your iron stores rather than the iron circulating at any moment, ferritin is widely used to check for both iron deficiency and iron overload.

What it can help assess

• Iron deficiency: a low ferritin level is the earliest and most reliable sign that your iron stores are running low, often before anaemia develops. This is a common cause of tiredness, weakness, and low energy
• Iron overload: a high ferritin level can indicate too much iron in the body, which may point to conditions such as haemochromatosis
• Monitoring iron levels: it is useful for tracking iron stores over time, for example during treatment for iron deficiency or in people who donate blood regularly

An important note on interpretation

Ferritin is also an acute phase protein, which means its level can rise temporarily in response to infection, inflammation, or illness, even when iron stores are normal. This can sometimes mask an underlying iron deficiency. For this reason, ferritin is often interpreted alongside other markers, such as a full blood count or other iron studies, and in the context of your symptoms and overall health.

Why it matters

Iron plays an essential role in carrying oxygen around the body and maintaining energy levels, so keeping it in the right range matters. Ferritin gives a clear picture of your iron reserves, helping to detect deficiency early or identify a possible iron overload. Any abnormal result is best discussed with your GP, who can consider the likely cause and advise on any further testing or treatment.