Early diagnosis and treatment reduce mortality in septic shock [17]. There is a need to develop new biomarkers to diagnose patients with septic shock as early as possible so that they can be treated quickly and mortality rates can be reduced.
In the univariate analysis of the current study performed in patients with septic shock, only the GCS score was statistically higher in the alive patient group. In contrast, age, lactate and CD64 values, the SOFA and APACHE II scores were statistically significantly higher in the dead patient group (p < 0.01). It was determined that the rate of patients diagnosed with respiratory distress was significantly higher in the dead patient group. This situation suggested that this is due to the high rate of patients diagnosed with respiratory distress.
Previous studies have shown that MR-PRO-ADM is a good biomarker for the diagnosis and prognosis of sepsis [18,19,20] and plays a key role in endothelial dysfunction in critically ill patients [21]. In addition, PRO-ADM has been shown to be highly concentrated in neonatal sepsis [22] and acute gout attacks with increased inflammation [12].
The mortality prediction of PRO-ADM in neonates undergoing postcardiac surgery (OR 14.1) [23] and the mortality prediction of our study (OR 15.86, p = 0.048) were similar. Guignant et al. [24] predicted 28-day mortality in their study on PRO-ADM in patients with septic shock. In the same study, the AUC value of PRO-ADM, measured in the first 1–2 days of septic shock, was 0.710 (95% CI, 0.584–0.835), whereas the AUC value of the present study was analyzed as 0.55 (95% CI, 0.40–0.70). Both studies predicted mortality similarly.
In another study [25] performed on patients with septic shock in the intensive care unit, although the AUC values of mid-regional pro-adrenomedullin (MR-PRO-ADM) of 0.730 and the cut-off value of 3.5 nmol/L differed from the AUC values of our study of 0.55 and the cut-off value of 86.79 pmol/, both studies predicted 28-day mortality.
It has been shown that PRO-ADM, which is useful for sepsis diagnosis [26], can predict mortality in septic shock. In the univariate analysis of the current study, there was no significant difference in PRO-ADM between dead and alive patients (p = 0.540). In contrast, multivariate analysis found that PRO-ADM predicted mortality (p = 0.048).
IL-6 has a moderate diagnostic AUC value of 0.81 (95% CI, 0.78–0.85) in critically ill patients with suspected infection [8], whereas it has a lower diagnostic AUC value of 0.77 (95% CI, 0.73–0.80) in patients with sepsis [27,28]. Our study's univariate and multivariate analysis found no significant difference in IL-6 levels among alive and dead patients. Considering that the IL-6 value is less than 7 pg/ml in healthy individuals [29], it is reasonable to assume that the high median value of IL-6 (77 pg/ml) in all patients in the current study is important for the diagnosis of septic shock but not for the prediction of mortality in patients with septic shock.
Studies have reported that CD64 is a poor prognostic factor in sepsis [27], bacterial infections [30), critically ill patients with sepsis [31], and neonatal sepsis (14). The AUCs of these studies were shown as 0.94, 0.92, 0.95, and 0.88, respectively, confirming the AUC value of the current study of 0.85 (95% CI, 0.75–0.95).
SOFA score [32,33], which is an essential parameter for predicting mortality in sepsis, was able to predict mortality in both univariate (p < 0.001) and multivariate analysis (p = 0.001) in the present study. It proved to be a statistically significant predictor of mortality, with an AUC value of 0.90 (95% CI, 0.82–0.98) in patients with septic shock. These results were similar to the SOFA score predicting 28-day mortality (AUC 0.84 (95% CI, 0.80–0.89); p < 0.001) in the study by Karakike et al. [33] in sepsis.
The fact that our study was conducted only in patients with septic shock and has a prospective design is the strength of the study, whereas the small sample size and the measurement of biomarkers only on admission are the weaknesses of the study. However, performing intermittent measurements might correlate better with clinical outcome.
In conclusion, serum CD64 level, PRO-ADM level, and SOFA score proved to be effective parameters for predicting prognosis and mortality in septic shock. However, IL-6 proved to be a weak biomarker and failed to predict mortality. CD64, which is easier and more practical to use, can be used instead of the SOFA score, which can be calculated by combining many parameters.