WBC
The white blood cell count (WBC, leukocyte count) is the number of immune cells in the blood. White cells defend the body against bacteria, viruses, fungi and parasites, clear damaged tissue and control inflammation. A raised count (leukocytosis) most often reflects infection, inflammation or stress; a low count (leukopenia, especially neutropenia) weakens the defence against infection. The differential — which types of white cells are increased or decreased — is essential for interpretation.
Types of white blood cells
White cells are produced in the bone marrow (lymphocytes also mature in the thymus, lymph nodes and spleen). Only a small part of them circulates in the blood at any moment; most are in tissues, the marrow reserve or attached to vessel walls. The five main types have different jobs:
Reference values
| Cell type | Absolute count, adults (×10⁹/L) | Increased in | Decreased in |
|---|---|---|---|
| Total WBC | 4.0–11.0 | Infection, inflammation, stress, smoking, leukaemia | Viral infection, drugs, marrow disease, autoimmunity |
| Neutrophils | 2.0–7.5 | Bacterial infection, steroids, trauma, surgery | Drugs, chemotherapy, viral infection, B12 deficiency, Duffy-null variant |
| Lymphocytes | 1.0–4.0 | Viral infections (EBV, CMV), pertussis, chronic lymphocytic leukaemia | HIV, steroids, acute stress, lymphoma, chemotherapy |
| Monocytes | 0.2–1.0 | Chronic infection (tuberculosis), recovery from infection, chronic myelomonocytic leukaemia | Aplastic anaemia, hairy-cell leukaemia |
| Eosinophils | 0.0–0.5 | Allergy, asthma, parasites, drug reactions, eosinophilic disorders | Steroids, acute stress |
| Basophils | 0.0–0.1 | Chronic myeloid leukaemia, myeloproliferative neoplasms, hypothyroidism | Rarely clinically important |
High WBC — leukocytosis
Most cases of leukocytosis are a normal reaction of the marrow to a stimulus. The pattern of the differential points to the cause:
- Neutrophilia — bacterial infection, tissue injury (burns, surgery, myocardial infarction), corticosteroids, smoking, obesity, intense exercise, pregnancy. A "left shift" (more young band forms) suggests acute bacterial infection.
- Lymphocytosis — viral infections (infectious mononucleosis), pertussis; persistent lymphocytosis in adults over 5 ×10⁹/L should be evaluated for chronic lymphocytic leukaemia.
- Eosinophilia — allergies, asthma, parasitic infections, drug reactions.
- Very high counts — a WBC above 50 ×10⁹/L may be a "leukaemoid reaction" to severe infection, but counts above 100 ×10⁹/L are almost always caused by leukaemia or a myeloproliferative disorder.
Immature cells (blasts) in the blood, a simultaneous fall in haemoglobin or platelets, very high counts without infection, unexplained weight loss, night sweats, fever, enlarged lymph nodes, spleen or liver. Such findings need a blood smear and prompt referral to a haematologist.
Low WBC — leukopenia and neutropenia
The clinically most important part of leukopenia is a low neutrophil count, because neutrophils are the first line of defence against bacteria and fungi.
| Absolute neutrophil count (×10⁹/L) | Severity | Infection risk |
|---|---|---|
| 1.0–1.5 | Mild | Usually not increased |
| 0.5–1.0 | Moderate | Moderately increased |
| < 0.5 | Severe | High — fever is a medical emergency |
Common causes are viral infections (often transient), medicines (antithyroid drugs, some antibiotics, antipsychotics such as clozapine, anticonvulsants, chemotherapy), vitamin B12 or folate deficiency, autoimmune diseases, an enlarged spleen and bone-marrow disorders. Many healthy people of African or Middle Eastern ancestry have a constitutionally lower neutrophil count linked to the Duffy-null blood-group variant; it is harmless and does not increase infection risk.
What affects the count
- Time of day and activity: counts are higher in the afternoon and after exercise or emotional stress.
- Smoking raises the WBC by about 1–2 ×10⁹/L on average.
- Corticosteroids raise neutrophils and lower lymphocytes and eosinophils within hours.
- Pregnancy raises the count, especially around delivery.
- Laboratory artefacts: nucleated red cells, clumped platelets or cold agglutinins can distort automated counts.
When to see a doctor
you have fever (38 °C or higher) or chills while your neutrophil count is low or you are receiving chemotherapy — this is febrile neutropenia and needs antibiotics within hours. Seek urgent care also for a very high WBC together with bleeding, breathlessness, confusion or severe fatigue.
the WBC or any cell type is repeatedly outside the reference range without an obvious temporary cause (cold, recent infection, steroids). Your doctor may repeat the count with a differential and blood smear, review your medicines and order further tests.
References
- Riley LK, Rupert J. Evaluation of patients with leukocytosis. Am Fam Physician. 2015;92(11):1004–1011. PMID: 26760415
- Chabot-Richards DS, George TI. Leukocytosis. Int J Lab Hematol. 2014;36(3):279–288. doi:10.1111/ijlh.12212
- Gibson C, Berliner N. How we evaluate and treat neutropenia in adults. Blood. 2014;124(8):1251–1258. doi:10.1182/blood-2014-02-482612
- Hsieh MM, Everhart JE, Byrd-Holt DD, et al. Prevalence of neutropenia in the U.S. population: age, sex, smoking status, and ethnic differences. Ann Intern Med. 2007;146(7):486–492. PMID: 17404350
- Arber DA, Orazi A, Hasserjian R, et al. The 2016 revision to the World Health Organization classification of myeloid neoplasms and acute leukemia. Blood. 2016;127(20):2391–2405. doi:10.1182/blood-2016-03-643544
This article is for general information and does not replace a consultation with a doctor. Interpret white-cell results together with your symptoms and a healthcare professional.
Published on 2 June 2019