Definition of Fever in Children
Fever in children is defined as a rectal temperature ≥38.0°C (100.4°F), which is the gold standard measurement method for accurate fever detection in young children. 1, 2
Temperature Thresholds by Measurement Site
- Rectal temperature ≥38.0°C (100.4°F) is the definitive threshold for fever and provides the closest approximation to core body temperature 1, 2
- The normal rectal temperature range is 36.7-37.9°C 2
- Rectal measurement remains the gold standard for children under 4 years of age 1, 2
Age-Appropriate Measurement Methods
Children Under 4 Years
- Rectal temperature is the preferred and most accurate method for infants and young children who cannot cooperate with oral measurement 2, 3
- This method is particularly critical when evaluating for serious bacterial infection or making important clinical decisions 3
Children 4 Years and Older
- Oral temperature is acceptable and preferred if the child can cooperate (hold thermometer under tongue with mouth closed) 2, 3
- If oral measurement suggests fever, confirm with rectal measurement before making critical clinical decisions if accuracy is essential 3
Critical Clinical Context
High-Risk Situations Requiring Immediate Evaluation
- All neonates with rectal temperature ≥38.0°C require immediate hospitalization with full sepsis evaluation due to 13% risk of severe bacterial infection 2
- Infants under 3 months with temperature ≥38.0°C are at highest risk 2, 4
- Infants 3-6 months with temperature ≥39.0°C warrant urgent evaluation 4
Important Measurement Pitfalls
- Recent antipyretic use (within 4 hours) can mask fever and severe infection, resulting in falsely normal temperatures 2
- Children may have severe infection despite normal or low temperature, especially after antipyretic administration 2
- Clinical appearance alone is unreliable: only 58% of infants with bacteremia or bacterial meningitis appear clinically ill 2
Special Considerations for Extreme Temperatures
- In heat-related illness contexts, rectal temperature >40°C (104°F) defines exertional heat stroke and requires immediate cooling interventions 5
- Heat exhaustion is characterized by core body temperature <40°C (104°F), while heat stroke involves temperatures ≥40°C with central nervous system dysfunction 5