With the number of patients increasing with years, sepsis has become a major focus and difficulty in the clinical management of patients with severe infections. Therefore, accurate and effective biomarkers of sepsis are of great significance to the treatment and prognosis. The mechanisms of the onset and progression of sepsis remain unclear, while the immune response is known a vital part that helps reduce the severity of inflammation. Immune-related biomarkers such as NLR, CRP, PCT, interleukins and chemokines have been widely applied to the early recognition and prognosis of sepsis [5–6]. Although the correlation between NLR and the prognosis of sepsis is currently controversial, there is a study which confirmed that elevation of NLR levels is independently correlated with poor clinical prognosis in patients with sepsis [7].
In this study, the ROC curve for assessing diagnostic value of the NLR was plotted with an AUC of 0.88, which demonstrated that the NLR could effectively distinguish healthy subjects from non-septic patients admitted to ICU, suggesting the diagnostic value of the NLR for sepsis. Beyond that, the NLR level was significantly higher in the sepsis death group compared to the survival group, which reflected that NLR is a potential predictor for the prognosis of sepsis. The cut-off value of NLR was 8.25 in the study, which was consistent with the cut-off value of 9.11 as reported by Ni[2] et al. We further observed NLR as an independent risk factor for 28-day mortality in patients with sepsis by univariate logistic regression analysis, which is consistent with the results demonstrated by Liu[8] et al., who found a positive correlation between NLR levels and the severity of disease in septic patients.
Currently, the diagnosis of sepsis relies on the SOFA scoring, which however fails in early diagnosis due to its tedious and time-consuming calculation mode, and is seldom applied in clinic as it is not well known by departments except the ICU. In this study, we found that the NLR had a great predictive value for the prognosis of sepsis, with the AUC of ROC curve of 0.77 and a sensitivity of 95.8%, which significantly outweighed the SOFA scoring. In addition, the NLR is easier to obtain and can be monitored in real-time, making it easier to carry out in clinical practice. The correlation analysis here also confirmed a positive correlation between the NLR level and SOFA scores.
CRP has been shown to facilitate the diagnosis of sepsis in relevant research [9]. As an indicator of inflammation, CRP has been used for many years to help monitor the condition of patients with chronic disease. Nevertheless, CRP lacks the specificity for the diagnosis of sepsis. In the study, adjusted univariate logistic regression analysis revealed that CRP could not be used as an independent risk factor for the prognosis of sepsis, with an AUC for prognostic efficiency of 0.65, which was significantly lower than that of the NLR and SOFA scoring.
PCT has been regarded as an indicator included in the diagnostic criteria for sepsis in the guidelines of Surviving Sepsis Campaign (SSC). A meta-analysis showed that the PCT test is more expensive compared to CRP test, but highly accurate for sepsis diagnosis. Another meta-analysis suggested that the sensitivity and specificity of PCT for distinguishing sepsis from non-infectious disease is 77% and 79%, respectively [5]. However, PCT levels can also elevate in non-infectious conditions, so clinical symptoms should be taken into consideration. This study also revealed a significant positive correlation between the NLR and PCT levels.
NLR is a research hotspot in recent years. It can be obtained by blood routine tests and is capable of reflecting the inflammation condition in the body. Current studies have shown that the NLR has clinical application value in cardiovascular, renal diseases and tumor [10–11]. In sepsis, lymphocytes decrease owing to the apoptosis mediated by innate immune response [12]. Reversely, the number of neutrophils dramatically increases in severe infectious diseases, especially in sepsis, reflecting the degree of inflammation. This might be mediated by the overexpression of the anti-apoptotic protein Mcl (myeloid cell leukemia) -1, which further suppresses the apoptosis of neutrophils [13], or due to the upregulation of granulocyte colony-stimulating factor (G-CSF) and the excessive release of chemokines, resulting in increased neutrophils [14]. In the present study, the NLR level elevated more significantly in the death group with severer inflammation, and the risk of death was significantly increased at NLR > 8.25 (OR = 6.39, P = 0.001), which also provided a theoretical foundation for our results.
There are some limitations in this study. Firstly, the study is a retrospective single-center study and the effect of selection bias cannot be excluded. Secondly, we only recorded NLR within 24 hours of admission while dynamic detection might be more preferable. Thirdly, the sample size is limited and inclusion of more samples or a multicenter study would be more convincing. Finally, this study focused on 28-day mortality without dynamic follow-up of patients, which could not obtain specific survival time for survival analysis, and further COX regression analysis with time variables. The classification of survival and death groups was simply based on the outcome, requiring additional supplement in our follow-up study.