Performance of the systemic immune-inflammation index in predicting survival to discharge in out-of- hospital cardiac arrest

Objective: To investigate whether the systemic immune-inflammatory index (SII) could be used as a prognostic marker of out-of-hospital cardiac arrest (OHCA). Methods: We evaluated patients aged 18 years and older, who presented to the emergency department (ED) due to OHCA between January 2019 and December 2021 and achieved the return of spontaneous circulation after successful resuscitation. Routine laboratory tests were obtained from the first blood samples measured following the patients' admission to ED. The neutrophil-lymphocyte ratio (NLR) and platelet-lymphocyte ratio (PLR) were calculated by dividing the neutrophil and platelet counts by the lymphocyte count. SII was calculated as platelets x neutrophils / lymphocytes. Results: Among the 237 patients with OHCA included in the study, the in-hospital mortality rate was 82.7%. The SII, NLR, and PLR values were statistically significantly lower in the surviving group than in the deceased group. The multivariate logistic regression analysis revealed that SII [odds ratio (OR): 0.68, 95% confidence interval (CI): 0.56-0.84, p = 0.004] was an independent predictor of survival to discharge. In the receiver operating characteristic analysis, the power of SII to predict survival to discharge [area under the curve (AUC): 0.798] was higher than either NLR (AUC: 0.739) or PLR (AUC: 0.632) alone. SII values below 700.8% predicted survival to discharge with 80.6% sensitivity and 70.7% specificity. Conclusion: Our findings showed that SII was more valuable than NLR and PLR in predicting survival to discharge and could be used as a pre-dictive marker for this purpose.