Utility of systemic immune-inflammation index as a serum biomarker to differentiate between complicated and simple para-pneumonic effusion

The systemic immune-inflammation index (SII) is a novel inflammatory biomarker. Simple and complicated para-pneumonic effusion (PPE) are two significant complications of pneumonia. We evaluated the efficacy of the SII to differentiate between the two. Records of all children up to 18 years of age admitted between April 2019 and September 2022 and diagnosed with simple or complicated PPE were retrospectively evaluated. SII and other biomarkers were compared between both groups. Receiver operating characteristics with the Youden index were used to estimate the discriminative value of SII. 50 children were enrolled with a median (interquartile range) age of 81.5 (36.7, 133.5) months; 31 (62%) were male. 31 (62%) had complicated PPE, and 19 (38%) had simple PPE. SII was significantly higher in complicated PPE (p=0.007). Good areas under the curve were found for C-reactive protein (0.771) and SII (0.736) to differentiate complicated from simple PPE. The best cut-off value for SII to differentiate complicated PPE from simple PPE was 1557×103μL, with a sensitivity of 82.4% and specificity of 57.6%. SII can be used as a screening tool to differentiate between complicated and simple PPE at the time of presentation.