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Iron and ferritin explained: what your results may mean

By Kerri Hopkins · 5 min read · 20 October 2026

Tiredness, low mood, anxiety, brain fog and hair changes are common and have many possible causes. Iron is one of them, and it is worth understanding what the markers on a blood test report can and cannot tell you.

What iron does

Iron helps your body make haemoglobin, the protein in red blood cells that carries oxygen. It also supports energy production, concentration and immune function.

Iron, ferritin and haemoglobin: what's the difference?

• Haemoglobin measures the oxygen-carrying protein in your blood. A low level can indicate anaemia.
• Serum iron measures iron circulating in your blood, which can change from hour to hour.
• Ferritin reflects your iron stores. It is often the most informative marker, but it can rise with inflammation or infection, so it is interpreted alongside other results.

Why you can feel unwell before haemoglobin changes

Iron stores can run low before haemoglobin drops. That means iron deficiency can be present without anaemia, and your doctor may look at several markers together rather than one.

Why a result can look "normal" and still leave you wondering

Every lab prints its own reference range, and the range is designed to describe most of the population rather than to say what is best for you personally. Some practitioners aim for higher levels than the lower end of a reference range, but UK guidance does not set a separate "optimal" range. If your result is within range and you still have symptoms, it is reasonable to ask your GP what else might be worth looking at.

Common reasons iron may run low

• Heavy or long periods
• Pregnancy and breastfeeding
• Diet low in iron-rich foods
• Conditions that affect absorption, such as coeliac disease
• Blood loss from other causes

Your GP can help work out which, if any, applies to you.

Everyday food ideas

• Iron-rich foods include red meat, poultry and fish, beans, lentils, tofu, fortified cereals, nuts, seeds and dark green leafy vegetables.
• Vitamin C, such as from citrus fruit, peppers or berries, can help your body absorb iron from plant foods.
• Tea and coffee with meals can reduce iron absorption, so some people leave a gap between them and iron-rich meals.

A note on supplements: please speak to your GP or pharmacist before starting iron tablets. Too much iron can be harmful, and the right type and dose depend on your test results.

Questions to take to your GP

• Which iron markers were tested, and what do they show together?
• What reference range does this lab use?
• Could anything be affecting my result, such as recent illness or inflammation?
• What could be causing low iron in my case, and should that be investigated?
• If I start treatment, when should I be retested?

Sources

NICE Clinical Knowledge Summaries: anaemia, iron deficiency.

BioHer provides educational information only. It is not medical advice, diagnosis or treatment, and it does not replace your GP or other healthcare professional. If symptoms feel urgent or severe, call 111 for urgent advice, or 999 in an emergency.