White blood cells are your immune system's front line. The white blood cell count (WBC) is included in every CBC and is one of the first clues to infection or inflammation.
What a high WBC means
A raised count, called leukocytosis, most often signals an active infection or inflammation. It can also rise with physical stress, smoking, steroid medication and, less commonly, blood disorders. The differential tells you more: high neutrophils point to bacterial infection, while high lymphocytes often accompany viral illness.
What a low WBC means
A low count, leukopenia, can follow viral infections, certain medications, autoimmune conditions or bone marrow problems. A very low neutrophil count increases vulnerability to bacterial infection and should be reviewed promptly.
The five types of white cell
- Neutrophils — bacterial defense
- Lymphocytes — viral defense and immune memory
- Monocytes — clean-up cells
- Eosinophils — allergy and parasites
Small fluctuations are normal. A single borderline value is rarely a concern on its own.
You don't have to interpret a single number alone. Upload your full lab report and Lab Lens will explain every value in plain English, or browse all our lab test guides.
This article is for general education only and is not medical advice. Reference ranges vary between laboratories — always read your result against the range on your own report and discuss it with your doctor.