Low red blood cells: causes and when to worry

With low red blood cells, haemoglobin is often low too: that is called anaemia. The most common cause is a lack of iron, but vitamin B12 or folate can be short too, or there may be blood loss. In pregnancy the count normally drops a little, because the blood gets more diluted.

What low red blood cells mean

It means there are fewer red cells in your blood than usual, so fewer cells to carry oxygen.

Haemoglobin is often low too: that is called anaemia. But it is haemoglobin that shows how marked it is, not the red cell count.

If your haemoglobin is normal and your red cells are just below the limit, it is usually nothing to worry about. Checking your ferritin and MCV as well may be enough.

What causes low red blood cells

They are the same as the causes of anaemia. The first is the most common.

Symptoms

If the drop is small, often none. When there is anaemia, you may notice:

These symptoms can have other causes too. And when anaemia comes on slowly the body adapts, so you can feel fine even with low numbers.

Low red blood cells in pregnancy

A small drop is usually normal. In pregnancy your blood volume grows, and the liquid part grows more than the red cells. So the count drops, especially from the second trimester on.

But pregnancy also needs a lot more iron, and a shortage is common. That is why your obstetrician checks your haemoglobin and, if needed, your ferritin, and decides whether you need a supplement.

If you feel very tired, short of breath or dizzy, tell your obstetrician.

Which tests to read alongside them

These tests help show whether there is anaemia and where it comes from.

What your result means

The lower end of the scale, in x10¹²/L. If they are low, check your haemoglobin too.

What to do if they are low

First find the cause, because the treatment depends on it. Where to start:

When to worry

Talk to your doctor if:

With Rosa, a haemoglobin below 11 g/dL is always flagged to a doctor, below 8 urgently.

Frequently asked questions

Low red blood cells: when should I worry? Talk to your doctor if your haemoglobin is low too, or the cause is not known. With a haemoglobin below 8 g/dL, see a doctor the same day. With black stools or blood in your stools, shortness of breath at rest, chest pain or fainting, call 112 or go to the emergency department.

Can low red blood cells be a sign of cancer? Usually not: the most common causes are too little iron, heavy periods or a pregnancy. In men and after menopause, if iron is short, doctors look first for blood loss from the stomach or gut. Sometimes that comes from a tumour, which is why anaemia should be checked by a doctor.

How can I raise my red blood cells? By treating the cause, which is why the tests come first. If there is anaemia from too little iron, you usually need a supplement set by your doctor, and food helps keep your store up. If vitamin B12 or folate is short, your doctor gives you that instead.

Low red blood cells in older people: is it normal? They become more common with age, but age alone usually does not explain them. Your doctor looks for the cause, such as too little iron, too little vitamin B12 or kidneys that filter less.

Do athletes have lower red blood cells? Sometimes, slightly: with a lot of endurance sport the liquid part of the blood grows and the count is diluted. But iron can be short too: ferritin helps tell.

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