White blood cell count

You do not need to do anything special before this test. A healthcare professional will take a blood sample from a vein in your arm. In babies, a small sample may be taken from the heel. 

What the test measures 

White blood cells (also called leucocytes) are part of your immune system. They protect your body by fighting infection and responding to illness. They are made in your bone marrow which is the spongy tissue inside your bones. 

There are five main types of white blood cells: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Each cell type plays a different role in keeping you healthy. The WBC count measures the total number of all these cells together. A separate test called a white blood cell differential count can show how many of each type you have. 

The typical reference range for adults is 4.0–11.0 x10⁹/​L, but your lab report will show the range used by your laboratory. Your doctor will tell you what your specific result means. 

Results vary depending on your age, time of day, and other factors. WBC counts are naturally higher in newborns and young children. Counts also tend to be slightly lower in the morning and higher in the afternoon. 

If your white blood cell count is high 

A high WBC count is called leucocytosis. A count of 11.0–17.0 x10⁹/​L is usually considered mildly to moderately raised. 

Common causes include: 

• infection, especially bacterial infections 
• inflammation caused by conditions such as rheumatoid arthritis 
• an allergic reaction 
• some medicines 
• recovery after surgery or injury 
• leukaemia and other bone marrow conditions 

Pregnancy can also raise your WBC count, particularly in the later stages. If you have had your spleen removed, you may have a mild but persistent rise in your count. 

Your doctor will look at your result alongside your symptoms to work out why your result is raised. 

If your white blood cell count is low 

A low WBC count is called leucopenia. A count of 3.0–4.0 x10⁹/​L is generally considered mildly low. A very low count can increase your risk of getting infections. 

Common causes include: 

• chemotherapy or radiotherapy 
• some medicines 
• bone marrow disorders 
• vitamin B12 or folate deficiency 
• liver disease 
• an enlarged spleen 
• some viral infections 
• autoimmune conditions such as rheumatoid arthritis or systemic lupus erythematosus (SLE) 

It is worth noting that older people sometimes do not show a raised WBC count even when they have an infection. Your doctor will take this into account when looking at your results. 

What happens next depends on your result and your symptoms. If your count is mildly raised or lowered but you feel well, your doctor may just want to repeat the test after a short time. 

If your result is more significantly abnormal, your doctor may refer you for further tests. These could include a blood film where a sample of your blood is viewed under the microscope, or other investigations to find out the cause. 

If you are already having treatment such as chemotherapy, a very low WBC count may mean your doctor adjusts your treatment plan. In some cases, you may be given an injection to help boost your white blood cell production.

Several things can affect your WBC count that are not related to illness. These include: 

• the time of day the sample is taken (counts are lower in the morning) 
• your age (newborns and infants naturally have higher counts) 
• pregnancy 
• medicines, including steroids, some antibiotics, and many other drugs 
• recent physical activity or emotional stress 

Always tell your doctor about any medicines you are taking, including over-the-counter and herbal remedies. 

Your doctor may also request: 

• a blood film, to look at the shape and appearance of your blood cells under a microscope 
• a repeat full blood count (FBC) which also measures red blood cells (RBCs), a white blood cell differential count and platelets 
• further tests depending on the suspected cause, such as blood cultures if an infection is suspected