Nonspecific Laboratory Tests as Possible Indicators of Complicated Community-Acquired Pneumonia in Children

Pneumonia is estimated to kill 1 million children under the age of five each year, mainly due to its complications, with 90%–95% of deaths occurring in developing countries such as Brazil. Chest radiography is a useful test for detecting complications or guiding invasive procedures, but this resource is not widely available across the country. Thus, nonspecific tests such as complete blood count and C-reactive protein (CRP) become important tools for diagnostic and prognostic assessment in infectious diseases. This study aimed to evaluate the association between leukocyte and CRP values and pneumonia complications in children. A retrospective, cross-sectional study assessed the association between leukocyte and CRP levels and pneumonia complications in children aged 0 to 11 years hospitalized in a hospital in the Center-South region of Paraná between 2018 and 2024. Patients who developed complications were compared to those who did not, with the following laboratory cutoffs: leukocytes ≥18,000 cells/mm³, neutrophils ≥50%, bands ≥10%, and CRP ≥20 mg/L, using tests collected within 24 hours of admission. Children were considered to have complicated pneumonia if they presented pleural effusion, pneumothorax, infected pneumatocele, or necrotizing pneumonia confirmed by chest X-Ray, with or without diagnostic thoracentesis. Statistical analysis was performed using chi-square and Fisher’s exact test. Of 558 medical records reviewed, 276 were included. Two hundred eighty-two patients were excluded because they did not have tests collected within 24 hours (122), stayed less than 24 hours in the hospital (52), were transferred (42), did not have pneumonia (30), were duplicates (27), or were admitted already with complications (9). Among the 276 included patients, 57 (20.7%) developed complications. Leukocytosis ≥18,000 cells/mm³ (OR = 4.97; p<0.05), neutrophil proportion ≥50% (OR = 9.96; p<0.05), band proportion ≥10% (OR = 4.11; p < 0.05), and CRP ≥20 mg/L (OR = 11.63; p<0.05) were associated with pneumonia complications. Literature shows divergent findings regarding leukocytosis and complications, but some studies correlate CRP with pleural effusion in community-acquired pneumonia. Elevated total leukocytes, neutrophils, band forms, and CRP levels are associated with complications of pneumonia in children.