Ferritin vs Haemoglobin: Why Normal Bloods Can Still Miss Low Iron

Two words do an enormous amount of damage in women's health, and they are "bloods" and "normal", usually in the same sentence.

You go to your GP (General Practitioner, your family doctor) because you are exhausted. They take blood. The result comes back as normal. And that would be the end of it, except that you still feel exactly the same as you did before anybody took any blood.

There is a specific, common and entirely fixable reason this happens, and it comes down to the difference between two numbers that sound similar and are not the same thing at all.

Haemoglobin is today. Ferritin is your savings.

Haemoglobin is the protein inside your red blood cells that carries oxygen around your body. It is measured as part of a full blood count, which is the standard test almost everybody gets. If your haemoglobin is low, you are anaemic. That is what the number is for.

Ferritin is different. Ferritin is a measure of the iron you have in storage. If haemoglobin is the money in your current account, ferritin is what is in the savings account behind it.

Here is the part that matters. Your body treats oxygen delivery as non-negotiable, so it will protect your haemoglobin for as long as it possibly can. It does that by quietly drawing down the savings. Your stores can fall a very long way while your haemoglobin stays comfortably in range, because the whole point of a reserve is that it gets used before anything visible changes.

Which means there is a stretch, and it can last months or years, where a full blood count looks completely unremarkable and your iron stores are nearly empty.

And ferritin is often not measured at all

This is the bit most people do not know. A standard full blood count does not automatically include ferritin. It has to be requested separately.

So when the text message says your bloods are normal, quite often what it means is that your haemoglobin is normal, along with your white cells and your platelets. Nobody has said anything untrue. It is simply a narrower statement than it sounds.

Hence the single most useful question you can ask: "Was my ferritin checked, or only my haemoglobin?"

Why this lands on women harder

None of this is subtle, and it is still routinely skipped over.

Menstruation is the largest ongoing draw on iron stores that most women have. Heavy periods increase that draw considerably, and "heavy" is chronically under-reported, largely because most women have nothing to compare their own experience against.

Then perimenopause arrives, and for a lot of women periods become heavier and less predictable for several years before they stop altogether. So the demand on iron stores can go up at precisely the point in life when everybody involved, including you, is inclined to say "it is probably my hormones" and leave it there.

Pregnancy, breastfeeding, a vegetarian or vegan diet, coeliac disease and some gut conditions all pull in the same direction.

What low stores actually feel like

Not a diagnostic list, and not something to score yourself against. These are simply the things that come up again and again, and they are easy to attribute to a busy life.

• Tiredness that sleep does not fix
• Being noticeably out of breath on stairs or a hill you used to manage without thinking
• Hair that is coming out more than it used to, particularly in the shower or the brush
• Difficulty concentrating, or a persistent feeling of thinking through fog
• Restless legs in the evening
• Feeling cold when nobody else in the room does

Any one of these on its own means very little. Several of them together, in a woman with heavy periods, is a reasonable prompt to ask a specific question rather than a general one.

Before you reach for a supplement

This matters more than anything below it, so it goes above the products rather than beneath them.

Do not start iron on a hunch. Iron is not a casual supplement. Taking too much causes its own problems, and taking it blind can flatten the very number somebody needed to see in order to work out what was going on. There are also conditions where extra iron is genuinely the wrong thing.

Get the number first. Then decide, ideally with somebody who can read it in context rather than against a printed range.

How to ask for it well

You are not demanding a test. You are giving somebody the information that makes the right test obvious.

Say what has changed and over what period. Say whether your periods are heavy, and be concrete about it: how often you change protection, whether you flood, whether you pass clots, how many days it lasts. That detail is far more persuasive than the word "heavy", which means something different to everybody.

Then ask the question plainly. "Was my ferritin checked, or only my haemoglobin?" And if it was not, "would it be reasonable to check it, given the periods?"

Ask for the actual figures rather than the word normal, and keep them. A number on its own tells you where you are. The same number six months later tells you which direction you are going, which is usually the more useful of the two.

If you have done all of that and got nowhere

Sometimes the honest answer is that ten minutes was never going to be enough, and you want somebody to sit down with the whole thing, results included, with time to actually read them.

That is what the Women's Health Consultation is for. Fifty minutes, your symptoms and whatever results you already have gone through properly, and a plan you can act on, including what to ask for next and who to ask.

This is general information, not personal medical advice, and it is not a substitute for seeing your own doctor. If you want someone to look at your own situation properly, that is what the Women's Health Consultation is for.