Low white blood cells: causes and when to worry

When your white blood cells are below your report’s limit, it is called leucopenia. It often comes from a recent virus or a medicine, and sometimes it is simply your normal level. The number that matters most is how many neutrophils you have: they are the white cells that defend you against bacteria.

What low white blood cells mean

White blood cells are the cells of your immune defences. When there are few of them, your body can find it harder to fight infections, especially if neutrophils are short.

Often the drop is mild and passes on its own, for example after a flu. Three things matter: how low your neutrophils are, whether the drop lasts, and whether your red cells or platelets are low too.

What causes low white blood cells

The first is the most common.

Symptoms

Usually none: they are often found by chance, on a blood test.

If your neutrophils are very low, infections can come more often or last longer: fever, mouth ulcers, a sore throat, skin infections.

If you have a fever and low white cells, see a doctor the same day. If your neutrophils are below 0.5, call 112 or go to the emergency department.

Low white blood cells and neutrophils: which one counts

Neutrophils are the largest share of your white cells, usually more than half, so when the total drops, they are often the ones missing. They are the first defence against bacteria: that is why they are the number that decides.

Your report usually shows them twice, as a percentage and as an absolute count (x10⁹/L). The absolute count is what matters: with a low total, a normal percentage can hide too few neutrophils.

If your neutrophils are normal and you feel well, a slightly low total is usually little cause for concern. Below 0.5 the risk of infection rises: see a doctor the same day. If you also have a fever, call 112 or go to the emergency department.

Which tests to read alongside it

These tests help find the cause.

What your result means

The lower end of the scale, in x10⁹/L. For the risk of infection, your neutrophil count is what matters.

What to do if they are low

It starts with your neutrophils and the cause. Where to start:

When to worry

Talk to your doctor if:

With Rosa, a neutrophil count below 0.5 x10⁹/L is always flagged to a doctor, urgently.

Frequently asked questions

Can low white blood cells mean cancer? Usually not: a recent virus, a medicine or a level that is normal for you is more often behind it. Rarely it comes from a bone marrow disease, such as leukaemia, and then your red cells or platelets are often low too. That is why, if they stay low, you should talk to your doctor.

Low white blood cells after chemotherapy: what to do? That is a different situation: chemotherapy lowers them for an expected period, and your oncologist decides which numbers to watch. If you get a fever during chemotherapy, call your treatment centre straight away or go to the emergency department.

Low white blood cells after a flu: is it normal? It happens often. Many viruses lower them for a while, then they come back up on their own. If they stay low, your doctor decides whether to repeat the test.

How do you raise white blood cells? By dealing with the cause: after a virus they usually come back up on their own, and if a medicine is involved, your doctor decides what to do. Foods and supplements usually do not help, unless you are short of vitamin B12 or folate: then your doctor decides the treatment.

How often should they be checked again? If you feel well, with your usual checks: Rosa measures them twice a year, with the blood count. If they are low, your doctor decides the timing.

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