White cell count

Some laboratories use 3.5 to 11 or 4 to 10; it is a little higher in pregnancy and in smokers; use the range your lab printed.

White blood cells are the cells of the immune system that circulate in the blood. The white cell count is the total number of all types together. The full blood count then splits this total into the different types, called the differential.

It is part of the full blood count. Doctors look at it when someone has an infection, inflammation or an unexplained illness, when monitoring medicines that can lower it, and when looking into blood and bone marrow conditions.

• Infection, particularly bacterial infection
• Inflammation from any cause
• Smoking
• Steroid medicines
• Stress, strenuous exercise and the hours after surgery
• Pregnancy
• Some blood and bone marrow conditions

• Viral infections
• Some medicines, including chemotherapy, some antibiotics and some used for arthritis, epilepsy and thyroid disease
• Low vitamin B12 or folate
• Autoimmune conditions
• Bone marrow conditions
• An enlarged spleen

• Strenuous exercise or emotional stress shortly before the test can raise it for a few hours
• Smokers sit a little higher in the general population
• People of African or Middle Eastern ancestry commonly sit a little lower in the general population, because of a lower neutrophil count, with no ill effect
• Steroid tablets raise it as an expected effect

No fasting needed. Best interpreted with the differential (the individual cell types) and, where relevant, repeated after recovery from any infection.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.