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Practice Rational Testing

Role of C reactive protein and procalcitonin in the diagnosis of lower respiratory tract infection in children in the outpatient setting

BMJ 2021; 373 doi: (Published 11 June 2021) Cite this as: BMJ 2021;373:n1409
  1. Andrés Pérez-López, assistant professor of clinical pathology and laboratory medicine1 2,
  2. Adam Irwin, senior lecturer in paediatric infectious diseases3 4,
  3. Carlos Rodrigo, associate professor of paediatrics5 6,
  4. Cristina Prat-Aymerich, assistant professor of medical microbiology7 8 9
  1. 1Divison of Microbiology Sidra Medicine, Doha, Qatar
  2. 2Weill Cornell Medical College in Qatar, Doha, Qatar
  3. 3UQ Centre for Clinical Research, The University of Queensland, Herston, Queensland, Australia
  4. 4Children’s Health Queensland Hospital and Health Service, South Brisbane, Queensland, Australia
  5. 5Department of Pediatrics, Hospital Universitari Germans Trias I Pujol, Badalona, Spain
  6. 6Autonomous University of Barcelona, Badalona, Spain.
  7. 7Department of Microbiology, Hospital Universitari Germans Trias I Pujol, Badalona, Spain
  8. 8CIBER Enfermedades Respiratorias, University Medical Center Utrecht, Utrecht University, Utrecht, the Netherlands
  9. 9Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht University, Utrecht, the Netherlands
  1. Correspondence to: A Pérez-López aperezlopez{at}

What you need to know

  • The difficulty of discriminating between viral and bacterial lower respiratory tract infection (LRTI) in children using clinical features alone often leads to overprescription of antibiotics

  • Biomarkers such as C reactive protein (CRP) and procalcitonin (PCT) have a limited capacity to rule in bacterial pneumonia in children in ambulatory settings where the prevalence of bacterial pneumonia is low. (CRP and PCT have limited diagnostic value in severely ill children who meet criteria for pneumonia or sepsis and who are candidates for broad spectrum antibiotic therapy)

  • There is growing evidence that antibiotic therapy can be safely withheld in children who are not severely ill with equivocal clinical presentation and low CRP (<20 mg/L) and PCT (<0.5 μg/L) levels

A previously healthy and fully vaccinated (including 13-valent pneumococcal conjugate vaccine) 22 month old boy is brought to the emergency department because of a 12 hour history of high fever (up to 40°C). He had had low grade fever, runny nose, cough, and decreased oral intake for the past two days. On examination, he did not look severely ill but was febrile (38.3°C). His respiratory rate was 45 breaths/minute (normal range 25-40 breaths/min at 18-24 months old), heart rate was 140 beats/minute (normal range 98-135 beats/min at 18-24 months), and blood oxygen level was 95%. Although breath sounds were not decreased, some bibasilar crackles were noted on chest auscultation. A chest x ray was interpreted as having bilateral peribronchial infiltrates and haziness in the right lower lobe. To aide their decision whether to initiate antibiotic therapy, clinicians requested blood tests, which revealed a white blood cell count of 22.5×109/L (60.0% neutrophils), a CRP of 30 mg/L (normal <5 mg/L), and a PCT of 0.25 μg/L (normal <0.5 μg/L).

Lower respiratory tract infections (LRTIs) in childhood are commonly of viral aetiology. Distinguishing viral from bacterial LRTI in children—and thus appropriately …

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