White blood cell count (WBC): high, low and what to do next

White blood cells, or leucocytes, are the cells of your immune system. Lab Tests Online UK explains that they are made in the bone marrow and that there are five main types: neutrophils, lymphocytes, monocytes, eosinophils and basophils. The white blood cell count adds all of them together and reports one total figure, expressed in billions of cells per litre of blood.

The total tells you the size of the army but not its make-up. A separate differential breaks the total down by cell type, and a rise in one family can be disguised in the total by a fall in another. For this reason doctors usually look at the total and the differential together.

The white cell count is nearly always requested as part of a full blood count. Lab Tests Online UK says you might have this test if your doctor thinks you could have an infection, an allergy or a problem with your immune system. It is also used to check for bone marrow conditions and certain rare blood disorders such as leukaemia, and to monitor treatments such as chemotherapy.

It can change from one day to the next, which makes it useful for following a condition. A falling count after antibiotics suggests the infection is settling, whereas a falling count during chemotherapy shows how the marrow is coping.

You do not need to do anything special beforehand. Blood is taken from a vein in the arm, and in babies a small sample may be taken from the heel. Lab Tests Online UK adds that results vary with age, time of day and other factors, with counts being lower in the morning and higher in the afternoon, and naturally higher in newborns and young children.

Recent exercise, emotional stress, pregnancy and many medicines including steroids and some antibiotics can also shift the count, so tell the person reviewing your results about anything that applies.

The typical adult reference range quoted by Lab Tests Online UK is 4.0 to 11.0 x10^9/L, but the same source is clear that your lab report will show the range used by your own laboratory and that your doctor will tell you what your result means. Treat any range you read online as a guide only.

A result outside the range is not automatically a problem. A figure that looks unusual in isolation may be entirely normal for you, and doctors consider symptoms, history and other results alongside it.

The common causes listed by Lab Tests Online UK are infection, especially bacterial infection, inflammation from conditions such as rheumatoid arthritis, an allergic reaction, some medicines, recovery after surgery or injury, and leukaemia and other bone marrow conditions. Pregnancy can also raise the count, particularly in later stages, and removal of the spleen can cause a mild but persistent rise.

Older people may not show a raised count even when they have an infection, so a normal figure does not rule one out in an unwell older adult.

Lab Tests Online UK lists chemotherapy or radiotherapy, some medicines, bone marrow disorders, vitamin B12 or folate deficiency, liver disease, an enlarged spleen, some viral infections and autoimmune conditions such as rheumatoid arthritis or lupus. The NHS adds antipsychotic medicines, medicine for an overactive thyroid and infections such as HIV or hepatitis, and says the main symptom of a low count is getting frequent infections.

A very low count can increase your risk of infection, and the NHS advises seeing a GP if you are at risk and develop an infection or if you keep getting infections.

If the count is mildly abnormal and you feel well, your doctor may simply repeat the test after a short time. More marked abnormalities lead to a blood film or investigation of the likely cause, such as blood cultures when infection is suspected. If you are having chemotherapy, a very low count may mean your treatment plan is adjusted, and in some cases you may be given an injection to boost white cell production.