✅ Leukocytosis is defined as a total white blood cell count (WBC) > 11 x 109/L..
✅ Neutrophilia is defined as an absolute neutrophil count > 7.7 x 109/L.
✅ Neutrophilia may be reactive or clonal.
✅ Causes of reactive neutrophilia include infection, inflammation, smoking, metabolic syndrome, solid tumor, medication, stress and splenectomy.
✅ A causal role of smoking in neutrophilia is supported by a dose-response relationship, with a larger effect seen in heavier smokers, as well as the fact that smokers’ higher WBC counts reverse rapidly after smoking cessation (typically within 8 weeks).
✅ Diagnosis is supported by normalization of counts upon smoking cessation.
✅ Smoking is associated with mild elevation of white cell count. If the white cell count/neutrophil count are greatly increased, other causes should be sought.