Hematology / CBC
White Blood Cell CountWBC
Total leukocyte count; meaningful only with the differential.
Sample
EDTA whole blood
Clinical reference range
4 to 11 ×10⁹/L
Adult
Conv: 4–11 ×10⁹/LFunc: 5–7.5 ×10⁹/L
Biology
What it measures
Granulocytes (neutrophils, eosinophils, basophils), lymphocytes, and monocytes have separate kinetics. Marrow produces ~10¹¹ neutrophils/day with a circulating half-life of 6–8 h.
Clinical use
Why we order it
Screen for infection, marrow disease, immunosuppression, leukemoid reactions, and steroid effects.
Lens · Clinical
Interpretation by lens
Clinical interpretation
Absolute neutrophil count (ANC) <0.5 ×10⁹/L is severe neutropenia; <0.1 demands neutropenic precautions.
Functional interpretation
WBC at the upper-normal end (>9) chronically reflects inflammation; investigate with CRP, fibrinogen, smoking status.
Research note
Neutrophil-to-lymphocyte ratio (NLR) is a robust prognostic marker across cancer, sepsis, and cardiovascular disease.
Differential
Causes of abnormal values
Causes of HIGH
- ↑Bacterial infection (neutrophilic, with left shift)
- ↑Steroids (demargination)
- ↑Stress, exercise, smoking
- ↑Leukemia/MPN (with abnormal differential or blasts)
- ↑Asplenia
Causes of LOW
- ↓Viral infection (often with relative lymphocytosis)
- ↓Drug-induced (chemotherapy, clozapine, propylthiouracil, methimazole)
- ↓Severe sepsis (neutropenic phase)
- ↓Marrow failure, infiltration
- ↓Benign ethnic neutropenia (common in people of African ancestry)
Pitfalls
Pre-analytic & interpretation traps
- !Always read the differential and the smear before reacting to WBC.
- !Benign ethnic neutropenia should not be 'worked up' as marrow failure.
Evidence-graded claims
What the data says
A
ANC drives infection risk during chemotherapy
Foundational, guideline-supported.
B
Neutrophil-to-lymphocyte ratio predicts outcomes in many diseases
Consistent association; specificity is low.
Related