Definition of Fever in Neutropenic Patients
Fever in a neutropenic patient is defined as either a single oral temperature ≥38.3°C (101°F) OR a sustained temperature ≥38.0°C (100.4°F) over a 1-hour period. 1, 2
Temperature Thresholds
The definition includes two distinct temperature criteria, either of which constitutes fever:
- Single measurement: One oral temperature reading of ≥38.3°C (101°F) in the absence of obvious environmental causes 1, 2
- Sustained measurement: Temperature ≥38.0°C (100.4°F) maintained for at least 1 hour 1, 2
Neutropenia Criteria
The fever definition applies when accompanied by specific neutrophil count thresholds:
- Absolute neutrophil count (ANC) <500 cells/mm³ is the primary criterion for neutropenia 1, 2
- ANC <1,000 cells/mm³ with predicted decline to <500 cells/mm³ also qualifies 2, 3
- Severe neutropenia is defined as ANC <500 cells/mm³ 1
- Profound neutropenia is defined as ANC <100 cells/mm³ 1
- Protracted neutropenia is defined as lasting ≥7 days 1, 2
Clinical Significance
This represents a medical emergency requiring urgent action:
- Empirical antibiotic therapy must be initiated within 2 hours of presentation 2
- At least half of neutropenic patients who become febrile have an established or occult infection 1, 2
- At least one-fifth of patients with neutrophil counts <100 cells/mm³ have bacteremia 1, 2
- Mortality rates range from 5% in solid tumors to 11% in hematological malignancies, and up to 18% in Gram-negative bacteremia 2
Important Clinical Caveats
Symptoms and signs of inflammation may be minimal or absent in severely neutropenic patients, making fever often the only indicator of serious infection. 1, 2 This occurs because neutropenia diminishes typical inflammatory responses, resulting in infections without typical cellulitis, pulmonary infiltrates without radiographic findings, or urinary tract infections without pyuria 1.