Evaluation of the efficiency of the systemic immune‐inflammation index in differentiating parapneumonic effusion from empyema

To evaluate the effectiveness of the systemic immune-inflammation index (SII) and other biomarkers in distinguishing parapneumonic effusion (PPE) and empyema.Patients who were thought to have pleural effusion secondary to pneumonia in the pediatric emergency department (PED) between 2004 and 2021 were retrospectively evaluated. The patients were divided into two groups as empyema and PPE. The efficacy of infection markers in predicting empyema was compared.Fifty-nine patients (59.3% male) were included in the study. Forty-three (72.9%) patients were in the PPE and 16 (27.1%) were in the empyema group. Length of hospital stay and pleural fluid thickness measured with thoracic ultrasonography were significantly higher in the empyema group (p = 0.018 and p = 0.002, respectively). The mean SII was 1902.73 ± 1588.87 in PPE patients, while it was 6899.98 ± 6678 in empyema patients (p = 0.009). C-reactive protein (CRP), white blood cell (WBC) count, absolute neutrophil count (ANC), and neutrophil-lymphocyte ratio (NLR) ​​were significantly higher in the empyema group; absolute lymphocyte count (ALC) and lymphocyte-monocytes ratio (LMR) were significantly lower than the PPE group. When the best cut-off values of inflammation markers are determined according to the area under the curve, the highest odds ratios suggesting empyema were found in SII, LMR, CRP, and ANC, respectively.Inflammation markers can be useful in predicting empyema. The best markers were found to be SII, LMR, CRP, and ANC. High SII is one of the practical diagnostic markers that can be used differentiate empyema from PPE in PED.