Although we could not demonstrate a positive correlation between serum level of YKL-40 and disease severity, the degree of reduction of YKL-40 levels on day 5 after admission could be considered as a prognostic biomarker and might guide the clinical decisions in children with pneumonia (e.g., need more intensive therapy and care, including mechanical ventilation or admission to ICU). This evidence concerns the gene CHI3L1 and susceptibility to pneumonia measurement.