Ferritin in women: why the normal range is not enough

Why your blood count does not see iron deficiency

Iron deficiency without anaemia is the most common nutrient deficiency worldwide, and at the same time the one that is overlooked most often. The reason: most doctors look at haemoglobin, the red blood pigment. As long as that is fine, the patient is considered healthy. But haemoglobin is the last value to fall. Your body empties the iron stores completely before it restricts oxygen transport.

And here is the decisive point: a ferritin of 19 ng/mL counts as normal at the GP. The reference range only starts at 15 ng/mL. In functional diagnostics that is already advanced iron depletion. A WHO systematic review shows: when the bone marrow is completely empty of iron, mean ferritin sits at 15.1 µg/L (Garcia-Casal et al., 2018 [1]). That means: the lower end of the standard reference range sits practically at the level of an empty store.

That is one of the reasons why aescolab does not only offer a standard blood count, but analyses up to more than 85 biomarkers, including ferritin, free T3 and vitamin D.

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Ferritin: why your iron store tells you more than haemoglobin

Ferritin below 50 ng/mL is, in current research, the threshold from which symptoms such as exhaustion can appear, even without anaemia. Your haemoglobin can be entirely normal while your iron store has long been in the cellar. The reason: your body needs iron for energy production in the mitochondria. When your ferritin falls, the mitochondria notice that long before anaemia develops. That explains why you are exhausted even though your haemoglobin looks normal.

A meta-analysis of six randomised controlled trials showed a significant therapeutic effect of iron on exhaustion in women with iron deficiency without anaemia, with an effect size of 0.33 (Yokoi & Konomi, 2017 [2]). All of these women had a normal blood count. What was not normal: their ferritin.

Lena’s ferritin sat at 19 ng/mL. According to the GP: normal. According to the research: an explanation for her exhaustion.

And that is exactly the dilemma: a reference range of 15 to 220 ng/mL is so wide that it waves almost everything through as “normal”. For ferritin, aescolab uses an optimal range of 50–130 ng/mL, clearly narrower than the standard reference range.

The studies: from which value does it become critical?

In a multicentre, randomised, controlled trial of 198 menstruating women with ferritin below 50 µg/L, exhaustion fell by 47.7% in the iron group, compared with 28.8% in the placebo group (Vaucher et al., 2012 [3]). The authors recommend explicitly: iron supplementation in women with unexplained fatigue and ferritin below 50 µg/L.

It is even clearer at very low values. A randomised study of 90 premenopausal women showed: at ferritin ≤15 ng/mL, intravenous iron improved exhaustion significantly; 82% of the iron group reported an improvement, compared with only 47% in the placebo group (Krayenbuehl et al., 2011 [4]). At ferritin between 16 and 50 ng/mL the effect was no longer statistically significant. That shows: the emptier the store, the clearer the effect.

Supplementing iron blindly can, however, cause harm when the store is already normal. Too much iron promotes oxidative stress. Measure first, then act: that is not a slogan, it is especially important with iron.

What iron deficiency does in the head

Iron deficiency without anaemia does not only affect energy. A study of 76 young women (18–22 years) showed: women with ferritin below 20 ng/mL had significantly higher scores for exhaustion, tension and irritability, even though their haemoglobin was normal (Sawada et al., 2014 [5]). The women with actual anaemia (Hb below 12 g/dL) did not show these psychological symptoms more strongly than those with normal haemoglobin. The decisive factor was not haemoglobin, but ferritin.

Lena knows that: the irritability in the afternoon, the feeling that her head can no longer keep up. She put it down to stress. In fact it was her iron store.

A systematic review confirms the picture: in 7 of 10 studies, cognitive performance improved after iron treatment in women of childbearing age, especially on tasks that require concentration and numerical skill (Greig et al., 2013 [6]).

The pattern is clear: do not wait until anaemia, but act when the store is emptying. The standard blood count does not see that, because it is not looking for it.

An extended analysis that specifically includes ferritin shows where you actually stand.

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Which ferritin value is actually optimal?

Optimal ferritin for women sits between 50 and 130 ng/mL. That is not an arbitrary range; it follows from the evidence: below 50 ng/mL symptoms appear; below 30 ng/mL diagnostic certainty for iron deficiency is very high (sensitivity 79%, specificity 98% according to a Cochrane review of 108 studies, Garcia-Casal et al., 2021 [7]).

A systematic review of 29 international guidelines concludes: for most clinical situations a ferritin cut-off of 100 µg/L should be considered, clearly above what most laboratories state as the lower limit (Peyrin-Biroulet et al., 2015 [8]). For young, healthy women with heavy menstruation, somewhat lower thresholds apply, but even here most guidelines recommend: below 30 µg/L is in need of treatment.

In the aescolab report you see standard and optimal side by side, so you recognise immediately where you sit in the grey zone. Not as a vague traffic light, but with concrete numbers and context.

Important: Ferritin is also an inflammation marker. In acute infections, chronic inflammation or after intensive sport the value can be temporarily raised and can mask true iron status. A CRP value helps to put that in context. aescolab tests both in the same panel.

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