MCH stands for mean corpuscular haemoglobin: the average amount of haemoglobin per red blood cell. Most Dutch labs report it between roughly 1.7 and 2.1 fmol (27 to 33 pg). A low MCH means your red cells are paler than expected, and the best known reason for that is a shortage of iron.
Every article on MCH gets that far. Then it stops.
What rarely gets said, and what matters most to an endurance athlete: your MCH can look perfectly fine while your iron store has been draining for months. I think that is the most misleading reassurance in the entire blood count.
What is the MCH value?
It is a calculation, not a separate measurement. The lab divides your total haemoglobin by your red blood cell count, and what remains is the amount of haemoglobin per cell. Where MCV says something about the size of your red cells, MCH says something about how full they are.
The two belong together. Small cells are usually pale cells, because less haemoglobin fits inside them. That is why MCV and MCH often move in the same direction.
So you rarely see a low MCH on its own. It usually arrives with company.
What does a low MCH mean?
Usually that your red cells contain too little haemoglobin, and the most common cause of that is iron deficiency. Iron is the building block of haemoglobin. With too little iron, your bone marrow makes cells that are smaller and paler than normal. In lab language that is microcytic and hypochromic.
Other causes exist. Thalassaemia, an inherited condition of haemoglobin production, gives a similar picture, and chronic inflammation can lock your iron away so it becomes unusable while your store looks normal on paper.
Imagine two runners, both with an MCH of 1.6 fmol. The first has a ferritin of 9 µg/l and trains six hours a week. The second has a normal ferritin but a family history around anaemia. The same MCH, two very different follow-up questions.
Why is a normal MCH not proof that your iron is fine?
Because your body gives up your haemoglobin last. Iron deficiency runs in stages: first your store empties, then the iron in your blood drops, and only once both are gone do your red cells start to look different. So your MCH changes late, and your haemoglobin later still.
That in-between stage has its own name: iron deficiency without anaemia. Your blood count looks normal, your MCH is fine, and your ferritin sits on the floor. Among university athletes that turned out to be far from rare (PMID 38018828), and in female endurance athletes the prevalence runs higher still (PMID 36554486).
That is exactly why the red cell indices are no substitute for a real iron measurement. Research placing them next to serum ferritin reached the same conclusion: as a surrogate they fall short (PMID 41160552).
| MCH | What it suggests | What you want to know alongside it |
|---|---|---|
| Low (below roughly 1.7 fmol) | Pale cells, often pointing towards iron deficiency | Ferritin and iron, and whether your haemoglobin drops with it |
| Normal, but you are tired and performance is sagging | Says little. An empty store can hide behind this | Ferritin, because it empties months earlier |
| High (above roughly 2.1 fmol) | Large, well-filled cells | Almost always judge together with MCV. Think B12 or folate |
| Low, with normal ferritin | Iron deficiency is less likely | Discuss with your GP. Chronic inflammation or thalassaemia may play a part |
The second row is where athletes come unstuck. A normal MCH feels like a green light, while nothing has been measured that shows your store.
How important is iron for your performance?
Iron sits at the heart of every haemoglobin molecule, and haemoglobin carries oxygen to your muscles. If your iron store drops, your oxygen transport eventually drops, and your endurance with it. That happens gradually, which is precisely why it is missed so often.
Endurance athletes also lose more iron than non-athletes: through sweat, through small bleeds in the gut, and in runners through damage to red cells in the soles of the feet (PMID 10688281). Add menstruation or a plant-based diet and the losses mount.
The Voedingscentrum notes that iron from meat is absorbed better than iron from plant sources. What you do with that is worth a conversation with your GP or dietitian, not a decision you take on a single lab value.
When should you discuss your MCH with your GP?
When your MCH is low, when your haemoglobin drops with it, or when you are tired and short of breath while your values look normal. The NHG guideline on anaemia describes the red cell indices as a starting point for further investigation, not an endpoint. A low MCH mainly tells you which question to ask next.
Do not take iron on your own initiative because your MCH sits on the low side. Excess iron accumulates, and that is not harmless.
My advice stays dull but useful: have your ferritin measured alongside it, and put the two numbers on the table together at your GP.
Where do you start?
Do not look at your MCH alone, but at its combination with ferritin and haemoglobin. Those three together tell a story none of them tells on its own. Our complete blood count test gives you MCH, MCV and the rest of the red series, with an assessment by a BIG-registered doctor.
How the whole series hangs together is in complete blood count explained. Why your haemoglobin can fall without anything being wrong is in low red blood cell count. And why endurance athletes in particular are at risk is in iron deficiency in athletes.
References
- Red blood cell indices versus serum ferritin as surrogate markers of iron deficiency. PLoS One. 2025. PMID 41160552.
- Predicting iron deficiencies using routine complete blood cell count parameters. Journal of Clinical Medicine. 2026. PMID 42355951.
- Prevalence of iron-deficient but non-anemic university athletes. Journal of the International Society of Sports Nutrition. 2023. PMID 38018828.
- High prevalence of iron deficiency in competitive female endurance athletes. International Journal of Environmental Research and Public Health. 2022. PMID 36554486.
- Fallon KE, Fallon SK, Boston T. Sports haematology. Sports Medicine. 2000. PMID 10688281.
- NHG. NHG guideline on anaemia. Accessed 2026.
- Voedingscentrum. Iron in the diet. Accessed 2026.
Disclaimer
Every blood test result includes a professional assessment by a BIG-registered doctor. This article gives general information and is not a substitute for medical advice. For treatment decisions, discuss your results with your GP.
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