High white blood cell count: what it means

What does the full blood count measure?

A full blood count measures the number and type of cells in the blood, including red cells, white cells and platelets. The test gives a total white cell count and a differential that splits white cells into types. Those types include neutrophils, lymphocytes, monocytes, eosinophils and basophils. Neutrophils are the main defence against bacterial infection.

What does a high white cell count mean?

A raised count is a non-specific signal, which means it does not point to one cause. A high count can indicate infection, inflammation, or leukaemia and other blood disorders. Infection, most often bacterial infection, is the most common cause. Results vary with age and time of day, and older people sometimes do not show a raised count even when they have an infection.

What else can raise it?

Inflammatory conditions such as rheumatoid arthritis can raise the count, and so can allergies. Some medicines, for example corticosteroids, can raise it. Physical or emotional stress can affect the white cell count. Smoking and pregnancy can also raise the count. Corticosteroids raise the white cell count by releasing neutrophils from the bone marrow into the circulation. A review says the white cell count can double within hours after stressors such as surgery, exercise, trauma or emotional stress, because of large neutrophil stores in the bone marrow and blood vessels.

What does the differential add?

A high neutrophil count usually suggests bacterial infection, inflammation or physical stress on the body. A high lymphocyte count can occur with viral infections or with conditions such as chronic lymphocytic leukaemia. Leukaemia and Hodgkin disease are among the conditions that can cause a high white cell count. Smoking commonly causes a mild rise in neutrophils, lymphocytes or both.

What happens next?

A hospital guideline from Hampshire says a mild, lasting rise is likely to come from a chronic inflammatory or infective process, or from smoking. The same guideline says an unexplained, very high count prompts an urgent referral to haematology. Doctors read the count with symptoms, the differential and sometimes a repeat test or a blood film. Reference ranges differ with age, sex and laboratory, so the report shows the range used. The NHS says severe breathing difficulty, or someone who has passed out and is not responding normally, needs a 999 call. MedlinePlus says some medicines, such as corticosteroids, can raise the white cell count, while others can lower it.

When might a blood disorder be considered?

A GP may arrange a blood test if leukaemia is suspected, and a very high white cell count could be a sign of it. In that case the person is referred urgently to a specialist in blood conditions, called a haematologist. UK sources list tiredness, bleeding or bruising easily, night sweats, weight loss and frequent infections among leukaemia symptoms. Cancer Research UK says leukaemia symptoms can be vague, and that minor conditions are common while leukaemia is rare. For chronic myeloid leukaemia the NHS advises a non-urgent GP visit if symptoms appear.