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Performance of blood biomarkers to rule out invasive bacterial infection in febrile infants under 21 days old
  1. Borja Gomez1,2,
  2. Haydee Diaz1,
  3. Alba Carro1,
  4. Javier Benito1,2,
  5. Santiago Mintegi1,2
  1. 1 Pediatric Emergency Department, Cruces University Hospital, Barakaldo, Spain
  2. 2 Department of Pediatrics, University of the Basque Country, Bilbao, Spain
  1. Correspondence to Dr Borja Gomez, Pediatric Emergency Department, Cruces University Hospital, Barakaldo 48903, Spain; borja.gomezcortes{at}


Objectives To determine the performance of procalcitonin (PCT), C reactive protein (CRP) and absolute neutrophil count (ANC) in identifying invasive bacterial infection (IBI) among well-appearing infants ≤21 days old with fever without source and no leukocyturia. To compare this performance with that in those 22–90 days old.

Design Substudy of a prospective single-centre registry performed between September 2008 and August 2017.

Setting Paediatric emergency department of a tertiary teaching hospital.

Patients 196 infants ≤21 days old and 1331 infants 22–90 days old.

Main outcome measures Sensitivity and negative likelihood ratio of blood tests for ruling out IBI (positive blood or cerebrospinal fluid culture). Abnormal blood test results: PCT ≥0.5 ng/mL, CRP >20 mg/L and ANC >10 000/µL.

Results Prevalence of IBI in infants ≤21 days old with normal or any abnormal blood test result was 3.6% and 6.8%, respectively (OR 0.52 (95% CI 0.13 to 2.01)), compared with 0.2% and 4.5% in older infants (OR 0.03 (95% CI 0 to 0.17)). Sensitivity and negative likelihood ratio of the blood tests for ruling out IBI in infants ≤21 days were 44.4% (95% CI 18.9% to 73.3%) and 0.79 (95% CI 0.43 to 1.44), respectively (vs 84.6% (95% CI 57.8% to 95.7%)%) and 0.19 (95% CI 0.05 to 0.67) in older infants). The values improved in infants with fever ≥6 hours aged 22–90 days, but not in those ≤21 days.

Conclusions PCT, CRP and ANC are not useful for ruling out IBI in febrile infants ≤21 days old. It is still recommended that these patients are admitted and given empirical antibiotic therapy, regardless of their general appearance or blood test results.

  • infectious diseases
  • neonatology

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  • Contributors BG conceptualised and designed the study, coordinated and supervised data collection, carried out the initial analyses, drafted the initial manuscript and reviewed and revised the manuscript. HD and AC collected data, carried out the initial analyses and reviewed and revised the manuscript. JB critically reviewed the manuscript. SM designed the data collection instruments and reviewed and revised the manuscript. All authors approved the final manuscript as submitted and agree to be accountable for all aspects of the work.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent Not required.

  • Ethics approval The prospective registry was approved by the Ethical Committee of Cruces University Hospital.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement Any unpublished data may be requested from the corresponding author.

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