Leukocyte ratios are useful early predictors for adverse outcomes of COVID-19 infection.

Leukocyte biomarkers, including the neutrophil-to-lymphocyte (NLR), monocyte-to-lymphocyte-(MLR), platelet-to-lymphocyte (PLR) ratios and systemic immune-inflammation index (SII) have been associated with severity and mortality of patients with COVID-19. The purpose of this study was to evaluate the association of baseline leukocyte biomarkers calculated in the emergency department (ED) with the disease severity and mortality. This was a retrospective cohort study that evaluated 1,535 (mean age 57+18 years) patients with SARS-CoV-2 infection in the ED of a single reference center. Outcomes were severity, defined as intensive care unit (ICU) admission requirement, and in-hospital mortality. All leukocyte biomarkers were calculated in the ED before the hospital admission. Their ability to predict the severity and mortality was measured using receiver operating characteristic (ROC) curves. Severity and mortality were observed in 30.9% and 12.6% of the patients, respectively, and were significantly correlated with NLR, MLR, PLR and SII, but only NLR was independently associated with both outcomes on multivariate analysis. Analysis of ROC curves revealed that NLR (0.78 for severity and 0.80 for mortality) and SII (0.77 for severity and 0.75 for mortality) had the best ability to predict mortality, when compared to other ratios. The highest AUC was observed for NLR, employing cut-off points of 5.4 for severity and 5.5 for mortality. Leukocyte biomarkers, particularly NLR, are capable of predicting the severity and mortality of patients with SARS-CoV-2 infection and could be important adjunct tools to identify patients in the ED that are more prone to develop adverse outcomes.