What is the definition of fever according to the latest guidelines?

Definition of Fever According to Latest Guidelines

According to the latest guidelines, fever in adult ICU patients is defined as a single temperature measurement greater than or equal to 38.3°C (101°F). 1

Fever Definitions by Patient Population and Setting

Different definitions of fever exist based on patient population and clinical setting:

• ICU patients: Single temperature measurement ≥38.3°C (101°F) 1
• Hospital-acquired infections: Temperature >38°C (100.4°F) per CDC 1
• Older adults in long-term care facilities: 1
  • Single oral temperature >37.8°C (100°F), OR
  • Repeated oral temperatures >37.2°C (99°F) or rectal temperatures >37.5°C (99.5°F), OR
  • An increase in temperature >1.1°C (2°F) over baseline temperature
• Neutropenic patients: 2, 3
  • Single oral temperature >38.3°C (101°F), OR
  • Temperature ≥38.0°C (100.4°F) sustained over a 1-hour period
• Pediatric patients: Temperature ≥38°C (100.4°F) 1

Preferred Temperature Measurement Methods

The accuracy of temperature measurement varies by method and should be selected based on clinical context:

• Central temperature monitoring methods are preferred when available: 1

  • Pulmonary artery catheter thermistors
  • Bladder catheter thermistors
  • Esophageal balloon thermistors

• For patients without central monitoring devices: 1

  • Oral or rectal temperatures are recommended over less reliable methods
  • Avoid axillary, tympanic membrane, temporal artery, or chemical dot thermometers due to lower accuracy

• For pediatric patients: 1

  • Rectal temperature is most accurate and closest to core temperature in neonates and young children
  • Oral temperature is preferred in older, cooperative children

Clinical Considerations

• Normal body temperature range is influenced by age, gender, diurnal variation, and measurement site 1
• Evidence indicates normal body temperature has been decreasing in humans by 0.03°C per birth decade over the last 157 years 1
• Not all infections manifest with fever; absence of fever in infected patients is associated with worse outcomes 1
• In older adults, infection should be suspected with new or increasing confusion, incontinence, falling, deteriorating mobility, reduced food intake, or failure to cooperate with staff, even in the absence of fever 1

Common Pitfalls in Fever Assessment

• Inconsistent temperature measurement methods: Different methods can yield significantly different readings; central thermometers and rectal measurements are more accurate than oral or axillary methods 1
• Failure to consider age-specific definitions: Older adults may have lower baseline temperatures and different fever thresholds 1
• Overlooking non-temperature signs of infection: Particularly in older adults, functional decline may be the only sign of infection 1
• Lack of standardized fever definition in clinical publications: Many publications use the term "fever" without specifying the minimum temperature, thermometer type, or measurement site 4

By understanding these population-specific definitions and measurement considerations, clinicians can more accurately identify fever and initiate appropriate diagnostic and therapeutic interventions.