What is Considered a High Temperature for Fever in a Child?
A fever in children is defined as a rectal temperature ≥38.0°C (100.4°F), and a high fever is considered ≥39.0°C (102.2°F). 1, 2
Standard Fever Definitions
The American Academy of Pediatrics establishes clear temperature thresholds for pediatric fever:
- Fever threshold: Rectal temperature ≥38.0°C (100.4°F) 1, 2
- High fever threshold: Temperature ≥39.0°C (102.2°F) 3
These definitions are consistent across emergency medicine guidelines and represent the standard for clinical decision-making. 3
Age-Specific Clinical Significance
The clinical implications of fever vary significantly by age:
- Infants <3 months: Any temperature ≥38.0°C (100.4°F) warrants immediate medical evaluation due to higher risk of serious bacterial infection 1, 4
- Infants 3-6 months: Temperatures ≥39.0°C (102.2°F) are particularly concerning 4
- Children >3 months: High fever is defined as ≥39.0°C (102.2°F), which triggers more aggressive diagnostic workup including consideration of occult infections 3
Measurement Method Matters
Rectal temperature is the gold standard for children under 3 years. 1, 2, 5 Other methods may underestimate true core temperature:
- Rectal: ≥38.0°C (100.4°F) defines fever 1, 2
- Oral: ≥37.6°C may warrant rectal confirmation 2
- Axillary: ≥37.2°C suggests fever 6
Clinical Context of High Fever
High fever (≥39.0°C/102.2°F) increases the likelihood of serious conditions:
- Occult pneumonia: 26% prevalence in children with fever ≥39.0°C and WBC >20,000/mm³ without respiratory symptoms 3
- Urinary tract infections: Higher prevalence with temperatures ≥39.0°C 3
- Bacteremia risk: Increases with higher temperatures, particularly in younger infants 3
Important Clinical Pitfalls
The height of fever alone does not predict serious illness—clinical appearance is paramount. 2 Common misconceptions include:
- Fever height does not correlate with febrile seizure risk 7
- Response to antipyretics does NOT indicate lower likelihood of serious bacterial infection 3
- Most high fevers (≥40.0°C/104°F) are still associated with common benign viral illnesses 7
Recent antipyretic use may mask true fever, making accurate temperature history essential. 1