White Blood Cell Count (WBC)
WBC is the total leukocyte concentration. The differential — neutrophils, lymphocytes, monocytes, eosinophils, basophils — adds specificity. Always interpret together.
What it measures
WBC reports total white blood cells per litre of blood. The body produces these in the bone marrow and uses them as the cellular arm of the immune response. Total WBC tells you whether the immune system is mobilised; the differential breakdown tells you which arm — neutrophil rise for bacterial infection, lymphocyte rise for viral, eosinophil rise for parasites or allergy, monocyte rise for chronic infection. Reading WBC without the differential is like reading total cholesterol without the LDL/HDL split.
What a high value can mean
- Bacterial infection — neutrophil-dominant rise, often with left shift.
- Viral infection — lymphocyte-dominant rise.
- Stress, exercise, corticosteroids — neutrophil rise without infection (demargination).
- Allergic disease, parasites — eosinophil rise.
- Leukaemia — extreme rise (often >50 × 10⁹/L) or abnormal cells on smear.
- Smoking — mild chronic elevation.
What a low value can mean
- Viral infection — particularly EBV, HIV, hepatitis.
- Chemotherapy, radiation, drug-induced — bone-marrow suppression.
- B12 or folate deficiency — pancytopenia possible.
- Autoimmune disease — lupus.
- Sepsis — paradoxically low WBC is a poor prognostic sign.
- Bone-marrow disease — aplastic anaemia, leukaemia (early).
- Benign ethnic neutropenia — common in people of African and Middle Eastern ancestry; no clinical significance.
When to discuss with a doctor
WBC <3 × 10⁹/L with absolute neutrophil count <1 × 10⁹/L carries infection risk and warrants prompt evaluation. WBC >25 × 10⁹/L (or any extreme value) warrants haematology referral. Mediora.AI reads WBC alongside the differential, platelets and CRP for context.