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When ‘Normal’ Blood Tests Miss Iron Deficiency

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Is it perimenopause… or something else?

In clinical practice, I’ve lost count of the number of women who think they must be going through perimenopause due to brain fog, tiredness, low mood and, at times, a total inability to string together a sentence.

You ask what they do for exercise. Cue the sheepish look — “I walk a bit… sometimes.”

Whilst these symptoms can of course be true of perimenopause, they also overlap with iron deficiency.


Iron deficiency: the missing conversation

However, iron deficiency rarely makes its way into the discussion. Current guidance allows HRT to be prescribed based on symptoms alone, even when FSH returns normal (i.e. when there are no diagnostic markers indicative of perimenopause).

For some, symptoms improve marginally and they assume that’s the best they’re going to get. But what can be underlying is iron deficiency. The symptoms are frustratingly similar.

And whilst I am glad that, nowadays, access to HRT is easier — I do have concerns.


A common problem hiding in plain sight

The Global Burden of Disease study, led by the Institute for Health Metrics and Evaluation at the University of Washington, places iron deficiency anaemia among the leading causes of disability in women of reproductive age globally.

A recent UK study by Randox Health found that almost one in three women had absolute iron deficiency — meaning their iron stores were insufficient for their needs.

So it’s often not a surprise when we look at a patient’s blood work and discover a ferritin level of 21.

When we begin to discuss iron deficiency, there are often questions about why this wasn’t picked up by their GP. And this is where it gets tricky…


When ‘normal’ blood tests aren’t normal

According to NICE guidance, ferritin levels below 30 µg/L are consistent with iron deficiency. However, laboratories often interpret results differently, meaning this may still be reported as “within range.”

In some cases, ferritin is only flagged as abnormal when it falls below 10–15 µg/L.

And in the same way that it can be pot luck whether you see a GP with additional training in fertility, the same can apply to iron deficiency.


Iron deficiency vs anaemia: not the same thing

Medical students spend relatively little time learning about iron deficiency in depth. GPs are primarily trained to identify anaemia, which means earlier stages of iron deficiency can be overlooked.

Iron deficiency is a condition in its own right — and a very common one.

The World Health Organisation classifies it as a major public health issue, particularly for women of reproductive age.

So what’s the difference?

When doctors run blood tests for these symptoms, they typically look at:

  • Full blood count
  • Ferritin
  • Thyroid function

Within a full blood count is haemoglobin (Hb) — a protein inside red blood cells that carries oxygen to tissues.

When ferritin levels fall for a prolonged period, haemoglobin eventually drops below range. This is anaemia — and it’s what GPs are trained to detect.

At that stage, there may be a conversation about iron supplementation.

But long before that point, there are signs that a person is already iron deficient.

According to NICE, ferritin below 30 µg/L indicates iron deficiency — even when haemoglobin is still normal.


The marker no one is measuring

There is, however, another marker that is rarely requested — and can offer even greater insight: transferrin saturation (TSAT).

Transferrin is a protein that transports iron. TSAT reflects the percentage of transferrin that is actually carrying iron.

In simple terms:

  • Ferritin tells us how much iron is stored
  • TSAT tells us how much is available for use right now

In functional iron deficiency, ferritin may appear normal or borderline, while TSAT is low.

If TSAT is never measured, it becomes difficult to fully assess a person’s iron status.


A system problem, not a clinician problem

It’s important to be clear here — this is not about blaming clinicians.

This level of nuance isn’t routinely taught, and often requires clinicians to seek out additional knowledge themselves.

The issue isn’t that iron deficiency is being ignored. It’s that the framework clinicians are working within isn’t always sensitive enough to detect it early — particularly in women.

And by the time anaemia is diagnosed, this represents a later stage of the process.

Earlier intervention may offer a more effective solution.


Too little, too late

Western medicine is often described as reactive, whereas traditional systems such as Chinese medicine are seen as preventative.

In the case of iron deficiency, intervention typically occurs once anaemia is present.

At that stage, oral iron supplements are often recommended. However, these are frequently poorly tolerated, particularly due to gastrointestinal side effects such as constipation.

For those unable to tolerate oral iron, intravenous iron infusion becomes the alternative.

But what if we identified and addressed iron deficiency earlier?


What other countries are doing differently

In some countries, iron deficiency screening is prioritised more proactively.

Australia, for example, has placed greater emphasis on iron status in women, and rates of anaemia are significantly lower than those seen in the UK.


The women’s health gap — and what’s missing

With the NHS Women’s Health Strategy aiming to address gaps in care, one might expect iron deficiency to be a key focus.

Yet, unlike menopause — widely discussed and supported — or endometriosis, which has gained increasing attention, iron deficiency remains relatively absent from the conversation.

It is one of the few areas where we can:

  • measure a problem
  • identify it early
  • and treat it effectively

And yet many women are still being told their results are “normal.”


The fertility link we can’t ignore

This becomes particularly relevant in fertility care.

A recent Finnish cohort study explored the impact of treating iron deficiency in women with infertility.

The study included 292 women with ferritin levels below 30 µg/L — importantly, all had haemoglobin within the normal range.

After treatment with intravenous iron and restoration of iron stores (typically within a few months), outcomes improved significantly:

  • Higher conception rates
  • A doubling of live birth rates
  • Substantially lower miscarriage rates

This is highly significant, particularly for couples labelled with “unexplained infertility.”

Because in many cases, blood tests may have been reported as normal — but iron deficiency was never fully assessed.


A final thought

At some point, we have to ask:

How much of “unexplained infertility” is truly unexplained?

And how much reflects limitations in what we choose to measure?

Because when it comes to iron deficiency, this begins to look less like unexplained infertility — and more like a failure to look closely enough.



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