Should I order laboratory tests for a high-grade fever in a well child?

Laboratory Testing for High-Grade Fever in a Well-Appearing Child

Laboratory tests are generally not necessary for a well-appearing child with a high-grade fever for only one day. 1

Decision Algorithm for Laboratory Testing in Febrile Children

Age-Based Approach

• For infants 0-28 days (neonates): Full sepsis evaluation including blood, urine, and CSF cultures is recommended regardless of appearance 1
• For infants 29-90 days: Risk stratification may allow for selective testing, but laboratory evaluation is still often warranted 1
• For children >3 months who are well-appearing: Laboratory tests are generally not indicated for a single day of fever without concerning symptoms 1, 2

Clinical Factors That Would Warrant Laboratory Testing

• Ill-appearing child regardless of fever duration 1, 3
• Fever ≥39°C (102.2°F) with duration >48 hours 1
• Specific signs of focal infection:
  • Respiratory symptoms (cough, rales, hypoxia, tachypnea out of proportion to fever) 1
  • Urinary symptoms, especially in girls 1, 2
• Immunocompromised status (e.g., cancer patients, transplant recipients) 1

Specific Laboratory Tests to Consider When Indicated

For Children with Specific Symptoms or Risk Factors

• Urinalysis and urine culture for:

  • Girls with fever ≥39°C (102.2°F) 1, 3
  • Any child with urinary symptoms 1
  • Infants <24 months with unexplained fever ≥48 hours 1, 2

• Complete blood count (CBC) for:

  • Fever ≥39°C (102.2°F) with duration >48 hours 1
  • Suspected bacterial infection based on clinical findings 4

• Chest radiograph only for:

  • Presence of respiratory symptoms (cough, rales) 1
  • High fever (≥39°C) with duration >48 hours 1
  • Tachycardia and tachypnea out of proportion to fever 1, 5

Evidence Quality and Common Pitfalls

Evidence Limitations

• Most studies show that the majority (58.6%) of ED visits for fever without source in children 3-36 months do not involve any laboratory testing 2
• The yield of laboratory testing in well-appearing children with brief fever is very low 1, 2

Common Pitfalls to Avoid

• Obtaining unnecessary laboratory tests in well-appearing children with brief fever duration can lead to:

  • Increased healthcare costs 5
  • Unnecessary pain and distress for the child 6
  • Potential false positive results leading to additional unnecessary testing 3
  • Parental anxiety 1

• Bag urine specimens are unreliable for diagnosis of UTI due to high contamination rates (26% vs 12% for catheterized specimens) 1, 3

• Assuming a normal WBC count rules out bacterial infection, as this can be misleading especially in young infants 3, 4

Special Considerations

• For prolonged fever (>3 weeks), a more extensive laboratory evaluation is warranted 4, 7
• In children with fever and suspected viral illness (e.g., bronchiolitis), chest radiographs are not recommended 1
• Urinary tract infections are the most common serious bacterial infection in febrile children, accounting for >90% of serious bacterial illness 3, 8