COVID-19 has been prevalent in many countries in the world, and the number of deaths is rising daily. Identification of early warning signs for severe COVID-19 and timely intervention may become urgent issues.
The results of the present study showed that there were significant differences in age, cancer incidence, NLR, CRP and albumin between the severe COVID-19 patients and mild COVID-19 patients, and there was a positive correlation between age, cancer, NLR, CRP and severe COVID-19 (P < 0.05) and a negative correlation between albumin and severe COVID-19 (P < 0.05). In the multivariate analysis logistic regression model, significant independent predictors for severe COVID-19 included a high NLR (OR=1.319, 95% CI: 1.043-1.699, P = 0.021) and albumin level (OR=0.739, 95% CI: 0.616-0.886, P = 0.001), which was in accordance with previous studies (14-16). NLR and albumin, associated with inflammation and tumor burden, were also revealed to be significantly related to survival in previous studies (16-18). The AUC calculated from the ROC curve was 0.851 (95% CI: 0.762-0.940), and the corresponding best cutoff value of NLR was 4.939, sensitivity was 0.700, and specificity was 0.917, which indicates high predictive value.
Neutrophils, important immune cells of the body, play the role of host defense and immune regulation when the body is invaded by infective agents (19). When neutrophils decrease significantly, the risk of infection increases significantly (20). Lymphocytes, the main effector cells of the human immune response, are closely related to the immunity and defense of the body; accordingly, there is a negative correlation between the number of lymphocytes and the degree of inflammation (21, 22). The NLR, the ratio of neutrophils to lymphocytes, is considered an important marker of the systemic inflammatory response, and more accurately reflects the balanced relationship between the severity of inflammatory reactions and the immune state (23, 24). It is believed that the inflammatory cytokine storm may be related to the progression of the disease (25-28). We speculate that there may be a significant correlation between the NLR and severe COVID-19. Huang et al. (8) reported that ICU patients had higher plasma levels of inflammatory cytokines such as IL-2, IL-7, IL-10, GCSF, IP10, MCP1, MIP1A and TNF-α than non-ICU patients, which reflected the obvious inflammatory reaction in severe and critical patients and was consistent with our results. An ambispective cohort study by Li et al. indicated that high cytokine levels, such as IL-2R, IL-6, IL-10, and TNF-α, were significantly associated with severe COVID-19 on admission (29).
At present, the reported risk factors for the severity of COVID-19 include older age, a longer wait for access to medical care, comorbidities, elevated proinflammatory cytokine levels, high LDH levels, and high procalcitonin and D-dimer levels (26, 29, 30). Most of the risk factors are not widely used because of their low sensitivity and difficulty in rapid evaluation. Therefore, there is an urgent need for simple and convenient predictive indicators to guide clinical practice. It is convenient in routine blood draws to obtain NLR, which has higher specificity and sensitivity for the early diagnosis of severe COVID-19.
In conclusion, the NLR at diagnosis was an independent risk factor for severe COVID-19 and may be an early warning sign for severe COVID-19 during clinical care. Further prospective studies with a large number of participants are necessary to validate the predictive role of the NLR in COVID-19 patients.