Neutrophil-to-Lymphocyte Ratio Cut-Off Point for COVID-19 Mortality: A Retrospective Study

Abstract

Several months have passed since the onset of the COVID-19 pandemic. Multiple characteristics have been proposed as prognostic factors so far. This study aims to provide evidence on the association of neutrophil-to-lymphocyte ratio (NLR) at the hospitalization time and three desired outcomes (mortality, prolonged hospitalization, and intensive care unit [ICU] admission). We designed a single-centre retrospective observational study in Baharloo Hospital (Tehran, Iran) from 20 February to 19 April 2020. Patients with confirmed COVID-19 diagnosis via rt-PCR or chest CT imaging were included. Demographic and clinical data were obtained. The sample was divided into three groups, using tertile boundaries of initial NLR. The differences in mortality, comorbidities, hospitalization duration, drug administration, and ICU admission between these three groups were investigated. The identified confounding factors were adjusted to calculate the odds ratio of death, ICU admission, and prolonged hospitalization. Nine hundred sixty-three patients were included. In total, 151 and 212 participants experienced mortality and ICU admission, respectively. In multivariate logistic regression models, the adjusted odds ratio for mortality event in the second and third tertile of initial NLR after full adjustment were 1.89 (95% CI:1.07-3.32) and 2.57 (95% CI:1.48-4.43) and for ICU admission were 1.85 (95% CI:1.14-3.01) and 2.88 (95% CI:1.79-4.61), respectively. The optimal cut-off value of the initial NLR for predicting mortality was 4.27. Initial NLR can predict mortality and ICU admission in COVID-19 patients. Further investigations for curating the calculated cut-off can propose initial NLR as an indicator of poor prognosis for COVID-19 patients.

Albumin levels, mean platelet volume, and neutrophil lymphocyte ratio as predictors of COVID-19 outcomes

“…This result is in line with studies that higher NLR at admission is associated with an increased risk of death [34,35]. The study by Kheyri et al, 2022, showed that the first results of NLR upon admission to the hospital were independently significant (p < 0.0011) with death and care in the intensive care unit [35]. A retrospective cohort also showed significant results (p = 0.0147), where each unit increase in NLR was associated with an 8% increase in the risk of death [26].…”

“…The results of this study show a significant effect of NLR on the outcome of COVID-19. This result is in line with studies that higher NLR at admission is associated with an increased risk of death [34,35]. The study by Kheyri et al, 2022, showed that the first results of NLR upon admission to the hospital were independently significant (p < 0.0011) with death and care in the intensive care unit [35].…”

“…The body's inflammatory response tends to increase neutrophil production and accelerate lymphocyte apoptosis [22,34]. Lymphocytes express ACE2 receptors, which are the targets of the COVID-19 virus, especially during cytokine storm conditions, so the number of lymphocytes tends to decrease [35]. Meanwhile, an increase in neutrophils is also associated with bacterial co-infection, which usually accompanies viral infections due to a decrease in the overall immune system [22,26].…”

“…NLR can be used as a predictor of COVID-19 outcomes [11,35]. A study in Wuhan established that the cut-off point of NLR was 3.338 (AUC=0.963; 95% CI = 0.911-1.000; p<0.001) with a sensitivity of 100% and a specificity of 84% [11].…”

“…In Iran, the cut-off point of NLR was 4.27, which has a sensitivity of 70.2% and a specificity of 60.22% [35].…”