From the Guidelines
White blood cell (WBC) counts and differentials are crucial indicators of infection severity, with elevations above 14,000 cells/mm3 or a left shift (percentage of band neutrophils or metamyelocytes, 16%; or total band neutrophil count, 1500 cells/mm3) warranting a careful assessment for bacterial infection 1.
Infection Severity Indicators
The degree of WBC elevation often correlates with infection severity, and the presence of an elevated total band count, increased percentage of neutrophils, and band neutrophils can indicate bacterial infection 1.
- A normal WBC count ranges from 4,500-11,000 cells/μL, with elevations (leukocytosis) above 11,000 typically suggesting infection or inflammation.
- Neutrophilia (elevated neutrophils) with increased band forms (immature neutrophils) above 10% suggests active bacterial infection.
- Left shift, where immature neutrophils enter circulation, correlates with infection intensity.
- Extremely high WBC counts (>25,000) may indicate severe infections like sepsis, while very low counts (leukopenia) can signal overwhelming infection that has depleted immune resources.
Diagnostic Considerations
The neutrophil-to-lymphocyte ratio (NLR) provides additional insight, with values above 6-7 associated with poorer outcomes in severe infections.
- Serial WBC measurements are more informative than single readings, as they show response to treatment.
- While these markers help assess infection severity, they should always be interpreted alongside clinical presentation, vital signs, and other laboratory findings for a comprehensive evaluation of infection status 1.
Clinical Application
In clinical practice, a CBC count, including peripheral WBC and differential cell counts, should be performed for all suspected infections, particularly in older adult residents of long-term care facilities, to promptly identify and manage potential bacterial infections 1.
From the Research
White Blood Cell (WBC) Indicators of Infection Severity
The following WBC indicators are associated with infection severity:
- Elevated total WBC count: Although not a reliable biomarker for diagnosing bloodstream infection (BSI) 2, an elevated WBC count can indicate infection severity.
- Neutrophil-lymphocyte count ratio (NLCR): The NLCR may be a useful screening test for BSI when procalcitonin assays are not available 2.
- Band count: A band count greater than 10% can provide useful information in patients whose diagnosis of infection is uncertain, leading to a moderate increase in the likelihood of infection 3.
- Absolute neutrophil count (ANC): ANC appears to be more sensitive than band count in predicting bacterial infections, except in elderly and infant populations 4.
- Toxic granulation in neutrophils: Toxic granulation in neutrophils appears to be as sensitive as ANC in predicting bacterial infection 4.
Specific WBC Indicators for Different Patient Populations
- Infants aged ≤2 months: ANC and %ANC serve as better diagnostic markers of serious bacterial infection (SBI) than total WBC 5.
- Elderly patients: Band count has a greater sensitivity in predicting bacterial infections 4.
Limitations of WBC Indicators
- Traditional biomarkers, including lactate, WBC, neutrophil count, procalcitonin, and immature granulocyte count, have limited utility in predicting sepsis 6.
- The diagnostic accuracy of WBC indicators can vary depending on the patient population and the specific infection being diagnosed 2, 3, 4, 5, 6.