The five types
All white blood cells arise from hematopoietic stem cells in the bone marrow; they are far fewer than red cells but form the core of immunity. In 1882 Russian zoologist Élie Metchnikoff pushed a thorn into a starfish larva and watched cells gather to engulf it, founding the theory of phagocytes and earning a 1908 Nobel Prize. A routine blood test's differential count separates five kinds.
| Type | Share (approx.) | Main role |
|---|---|---|
| Neutrophils | 50–70% | First-line phagocytes against bacteria; main component of pus |
| Lymphocytes | 20–40% | T cells, B cells (antibodies) and NK cells; viruses and immune memory |
| Monocytes | 2–8% | Become macrophages in tissues; clean-up and antigen presentation |
| Eosinophils | 1–4% | Defence against parasites; allergy and asthma |
| Basophils | 0.5–1% | Release histamine in allergic reactions |
When the count is high
A count above about 10,000/μL is called leukocytosis. The most common cause is bacterial infection: neutrophils climb sharply in pneumonia or appendicitis. Steroid medicines, smoking, intense exercise or stress and pregnancy can also raise it temporarily. Raised eosinophils point first to allergy or parasites, raised lymphocytes to viral infection. Very high counts in the tens or hundreds of thousands with immature cells require evaluation for leukemia.
When the count is low
A count below about 4,000/μL is leukopenia. Neutrophils below 1,500/μL is neutropenia, and below 500 the risk of serious infection is high, so fever needs urgent care. Causes include chemotherapy, some drugs such as certain antibiotics and antithyroid medicines, viral infections, autoimmune disease and aplastic anemia. A result just outside the reference range at a check-up is not a diagnosis on its own, and some people of African or Middle Eastern ancestry naturally run slightly lower neutrophil counts. Doctors interpret repeat tests together with the differential.
This article is general health information and is not a substitute for diagnosis or treatment. If symptoms persist, see a doctor.
FAQ
- Should I worry about a slightly high white cell count?
- A cold, stress, smoking or exercise before the test can nudge it up. If other results and symptoms are normal, doctors often simply repeat the test in a few weeks.
- Are there foods that boost white blood cells?
- No specific food raises the count. A balanced diet with enough protein and sleep supports immune cell production; a markedly low count needs its cause found and treated.
Sources reviewed: 2026-10-26
References
- Janeway, C. A., et al. (2001). Immunobiology: The Immune System in Health and Disease (5th ed.). Garland Science.
- Metchnikoff, É. (1908). On the present state of the question of immunity in infectious diseases. Nobel Lecture.
- Bain, B. J. (2015). Blood Cells: A Practical Guide (5th ed.). Wiley-Blackwell.