The diagnostic value of platelet-to-lymphocyte ratio, monocyte-to-lymphocyte ratio, and neutrophil-to-lymphocyte ratio for sepsis: to provide early warning before clinical deterioration

Sepsis is a life-threatening organ dysfunction caused by the body’s abnormal immune response to infection.Current diagnostic criteria is affected by multiple clinical factors, resulting in a diagnostic delay.Objective To investigate the diagnostic value of platelet-to-lymphocyte ratio (PLR), monocyte-to-lymphocyte ratio (MLR), and neutrophil-to-lymphocyte ratio (NLR) in patients with sepsis, to provide a simple and practical laboratory index reference for the early diagnosis of sepsis. A retrospective cohort study was conducted on 18,570 patients from the MIMIC database (2015–2020). After screening, 11 858 patients were included and classified into sepsis ( n = 10 145) and control ( n = 1713) groups based on Sepsi3.0. Biomarkers measured within 24 h when admitted in Intensive Care Unit(ICU) before diagnosed with sepsis which were analyzed using logistic regression. Diagnostic performance was assessed by receiver operating characteristic (ROC) curves.Restricted cubic spline (RCS) logistic regression model to explore the nonlinear association between MLR and the odds ratio (OR) of sepsis. MLR and NLR in the sepsis group were significantly higher than those in the non-sepsis group (all P < 0.001). Multivariable logistic regression analysis identified that MLR (OR = 1.57, 95% CI: 1.40–1.74, p < 0.001) and NLR(OR = 1.01, 95% CI: 1.01–1.02, p < 0.001) was strongly and independently associated with sepsis. The ROC curves showed that the areas under the curve of PLR, NLR and MLR levels alone and in combination for predicting sepsis were 0.496, 0.545and 0.571, respectively. The RCS identified OR for sepsis remained consistently below 1.00 when MLR was less than 0.69. Beyond this threshold, the OR increased sharply above 1.00. Multivariable logistic regression analysis identified MLR and NLR were strongly and independently associated with sepsis after confounders are adjusted( P < 0.001).the markedly imbalanced study population substantially may influence ROC performance, MLR and NLR have a weak diagnostic value for sepsis as independent laboratory markers.The Restricted cubic spline logistic regression model (RCS) showed MLR > 0.69 could serve as a potential warning threshold for identifying patients at elevated sepsis risk, as simple and easy-to-obtain inflammatory ratios reducing misdiagnosis and missed diagnoses.