The association between the neutrophil-to-lymphocyte ratio and mortality in critical illness: an observational cohort study

Justin D Salciccioli, Dominic C Marshall, Marco AF Pimentel, Mauro D Santos, Tom Pollard, Leo Anthony Celi, Joseph Shalhoub

IntroductionThe neutrophil-to-lymphocyte ratio (NLR) is a biological marker that has been shown to be associated with outcomes in patients with a number of different malignancies. The objective of this study was to assess the relationship between NLR and mortality in a population of adult critically ill patients.MethodsWe performed an observational cohort study of unselected intensive care unit (ICU) patients using a large clinical database. We computed individual patient NLR and categorized patients by quartile of this ratio. The association of NLR quartiles and 28-day mortality was assessed using multivariable logistic regression. Secondary outcomes included mortality in the ICU, in-hospital mortality and 1-year mortality. An a priori sub-group analysis of patients with and without sepsis was performed to assess any differences in the relationship between the NLR and outcomes in these cohorts.ResultsA total of 5,056 patients were included with a 28-day mortality rate of 19%. The median age of the cohort was 65 years and 47% were female. The median NLR for the entire cohort was 8.9 (interquartile range: 4.99 to 16.21). Following multivariable adjustments, there was a stepwise increase in mortality with increasing quartiles of NLR (1st quartile: reference category; 2nd quartile odds ratio (OR)¿=¿1.36, 95% confidence interval (CI): 1.06 to 1.74; 3rd quartile OR¿=¿1.47, 95% CI: 1.15 to 1.89; 4th quartile OR 1.78, 95% CI: 1.41 to 2.25). A similar stepwise relationship was identified in the subgroup of patients who presented without sepsis. The NLR was not associated with 28-day mortality in patients with sepsis. Increasing quartile of NLR was statistically significantly associated with secondary outcomes.ConclusionThe neutrophil-to-lymphocyte ratio is associated with outcomes in unselected critically ill patients. In patients with sepsis there was no statistically significant relationship between NLR and mortality. Further investigation is required to understand the pathophysiology of this relationship and to validate these findings with data collected prospectively.