Background <p>Pediatric pneumonia remains a leading cause of under-5 mortality worldwide. Emerging evidence suggests that complete blood count (CBC) parameters may serve as predictive indicators for acute clinical deterioration. This study aimed to identify a cost-effective, rapid, and reliable biomarker for predicting adverse outcomes in pediatric pneumonia within outpatient and primary care settings.</p> Methods <p>This retrospective case-control study analyzed 15,359 pediatric pneumonia admissions at a tertiary hospital between 2015 and 2022. Using restricted cubic splines (RCS), multivariable logistic regression, and receiver operating characteristic (ROC) curve, this study evaluated the correlation between seven CBC parameters - hemoglobin (Hb), platelet (PLT), neutrophil-to-lymphocyte ratio (NLR), red cell distribution width (RDW), absolute neutrophil count (ANC), lymphocyte absolute value (LYM), and white blood cell count (WBC) - and adverse outcomes in pediatric pneumonia.</p> Results <p>Severe cases exhibited reduced Hb, PLT, and LYM (all <i>P</i> &lt; 0.001) and elevated RDW, ANC, and NLR (all <i>P</i> &lt; 0.001). Multivariable logistic analysis identified Hb and PLT as independent negative predictors, while NLR and RDW as independent positive predictors for adverse outcomes (<i>P</i> &lt; 0.001). NLR demonstrated superior predictive performance, followed by Hb. Combining NLR and Hb significantly enhanced predictive capacity.</p> Conclusions <p>We found that CBC parameters, particularly NLR and Hb, were robust, accessible predictors of adverse outcomes in pediatric pneumonia. Their integration into risk stratification protocols could optimize clinical decision-making, especially in resource-limited settings.</p> Impact <p><UnorderedList Mark="Bullet"> <ItemContent> <p>This study identified Hb, PLT, NLR, and RDW as independent predictors of adverse outcomes in pediatric pneumonia.</p> </ItemContent> <ItemContent> <p>NLR demonstrated the strongest predictive performance, and its combination with Hb significantly enhanced risk stratification</p> </ItemContent> <ItemContent> <p>These low-cost, readily available indices offered a practical tool for rapid triage in primary care and resource-constrained settings.</p> </ItemContent> </UnorderedList></p>