Neutropenia Definition and Classification
Neutropenia is defined as an absolute neutrophil count (ANC) less than 1,500 cells/μL, with severity increasing as the count decreases below this threshold. 1
Severity Classification
Neutropenia can be classified by severity according to the absolute neutrophil count:
| Grade | Neutrophil Count |
|---|---|
| 0 | ≥2,000 cells/μL |
| 1 | 1,500-2,000 cells/μL (mild) |
| 2 | 1,000-1,500 cells/μL (mild) |
| 3 | 500-1,000 cells/μL (moderate) |
| 4 | <500 cells/μL (severe) |
The most clinically significant classifications include:
- Mild neutropenia: ANC 1,000-1,500 cells/μL
- Moderate neutropenia: ANC 500-1,000 cells/μL
- Severe neutropenia: ANC <500 cells/μL
- Profound neutropenia: ANC <100 cells/μL 1, 2
Clinical Significance
The clinical significance of neutropenia directly correlates with its severity:
- Risk of infection: The frequency and severity of infection are inversely proportional to the neutrophil count 3
- Severe infection risk: Greatest when ANC <500 cells/μL
- Bloodstream infection risk: Highest when ANC <100 cells/μL (approximately 10-20% of patients) 3
- Infection sites: Primary sites include the alimentary tract (mouth, pharynx, esophagus, bowel, rectum), sinuses, lungs, and skin 3
Important Considerations
Infection Risk Factors
- The risk of infection significantly increases when ANC falls below 500 cells/μL 3, 1
- The duration of neutropenia and rate of decline are critical factors affecting infection risk 3
- Febrile neutropenia (≥38.3°C orally or ≥38.0°C over 1 hour) is a medical emergency requiring immediate antibiotic therapy 3, 1
Pathogens
- Early infections: Primarily bacterial (coagulase-negative staphylococci, S. aureus, viridans group streptococci, enterococci, E. coli, Klebsiella, Pseudomonas aeruginosa)
- Later infections: Antibiotic-resistant bacteria, yeast, fungi, and viruses 3
Management Considerations
- Severe neutropenia (ANC <500 cells/μL) may require prophylactic use of colony-stimulating factors to reduce risk, severity, and duration of febrile neutropenia 3
- Profound neutropenia (ANC <100 cells/μL) requires immediate intervention including G-CSF therapy and infection prevention measures 1
- Febrile neutropenia requires prompt administration of broad-spectrum antibiotics 1
Pitfalls to Avoid
- Don't ignore neutropenia, even if mild, in patients receiving myelosuppressive chemotherapy as it may progress to more severe forms
- Don't overlook the importance of the rate of decline in neutrophil count, not just the absolute value
- Remember that signs and symptoms of infection may be absent or muted in neutropenic patients, but fever remains an important early sign 3
- Avoid delaying treatment in febrile neutropenia as it is associated with increased morbidity and mortality
Neutropenia is a significant clinical finding that requires appropriate assessment of severity and risk factors to guide management decisions and prevent serious infectious complications.