White Blood Cell Count (WBC)

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.

• Adults: about 4.0-11.0 x10^9/L, similar across sexes.
• The differential matters as much as the total: neutrophils ~40-75%, lymphocytes ~20-45%, monocytes ~2-10%, eosinophils ~1-6%, basophils <1-2%.
• Some people of African and Middle Eastern ancestry run a benignly lower count.

Your lab's printed range is what counts.

• 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.

• 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.

• WBC itself gives no direct symptoms - what you feel comes from the cause.
• High WBC with an infection brings fever, aches or local signs; very low WBC raises infection risk, so recurrent or severe infections are the warning.
• Read the total with the differential, platelets and CRP for the real picture.