Low ferritin: the tiredness that gets missed

A woman comes in exhausted. Climbing the stairs is harder than it was. Her hair is coming out more than it should. She is cold when nobody else is, and her concentration has gone. She has been tested for anaemia and told she is not anaemic.

Both things can be true at once, and the reason is worth understanding.

Haemoglobin and ferritin are not the same test

Haemoglobin measures the oxygen carrying protein in your blood right now. Ferritin is a rough measure of how much iron you have in storage.

Think of it as a bank account. Haemoglobin is whether today's payment cleared. Ferritin is what is left in savings.

Your body will protect haemoglobin for as long as it can, drawing down stores to do it. So iron stores can fall a long way before the full blood count shows anything at all. By the time you are formally anaemic, the savings have usually been empty for a while.

If only haemoglobin was checked, low stores can be missed entirely.

Why women run low

This is not a rare or exotic problem, it is arithmetic.

• Menstrual loss. Every period costs iron. Heavy periods cost considerably more, and heavy is chronically under-reported because women compare themselves with nobody.
• Pregnancy. Each one draws heavily on stores, and they are not always replaced afterwards.
• Intake. Iron from plant sources is absorbed far less efficiently than iron from meat. Eating well is not the same as absorbing well.
• Absorption. Coeliac disease, inflammatory bowel conditions and some stomach conditions reduce how much you take up. Tea and coffee with meals reduce it further.
• Perimenopause. Cycles often become heavier and less predictable in the 40s, at exactly the point women are least likely to be checked.

Put those together across 20 or 30 years and stores can drain quietly while every individual year looks unremarkable.

What low stores can feel like

• Fatigue that rest does not fix
• Breathlessness on stairs or hills that used to be easy
• Hair shedding, and hair that has become finer
• Brittle or spoon shaped nails
• Poor concentration and low mood
• Feeling the cold more than the people around you
• Restless legs at night
• Headaches, or a racing heart on exertion

Every one of these has other explanations. That is precisely why it gets missed. Each symptom on its own looks like life, or stress, or age.

The complication worth knowing about

Ferritin is also an acute phase protein, which means it rises with inflammation, infection and some chronic conditions. Someone can have genuinely depleted iron stores and a ferritin result that looks acceptable, because inflammation has pushed it up.

This is one of the clearest examples of why a number needs reading alongside the person. A ferritin result interpreted in isolation, with no view of inflammatory markers, symptoms or history, can be quietly misleading. It is usually read alongside a full blood count and inflammatory markers for exactly this reason.

Sensible questions to ask

• Was ferritin actually measured, or only haemoglobin and the full blood count?
• What was the number? Not just whether it was flagged. Where it sits in the range matters.
• Were inflammatory markers checked at the same time? Without them, a middling ferritin is hard to interpret.
• If it is low, why? Low iron is a finding, not a diagnosis. The question of where it is going always deserves an answer, particularly after menopause or where there is any bowel symptom.

An important caution

Iron is not a supplement to take speculatively. Some people carry conditions where iron accumulates and taking more is actively harmful, and taking iron before testing can obscure the picture. Test first, treat on the result, and find out why it was low.

Where this gets looked at properly

At-home Blood Test

Including the markers that get left off

Initial Consultation

Because low iron is a finding, not an answer

Lifestyle Medicine Consultation

Food, absorption and the daily detail

The point

Not being anaemic is not the same as having enough iron. If you are exhausted, losing hair and breathless on the stairs, ferritin is a fair thing to ask about, and the number itself is worth seeing.