COVID-19 was an acute novel respiratory infectious disease. The disease was first reported in Wuhan, China, and had spread across the world. The source of infection was mainly SARS-cov-2 virus- infected persons, the virus also could be spread by people who had experienced no symptoms, and almost everyone had no immunity to the disease [8]. In our study, the age distribution ranged from one to eighty-three years old; the age of severe patients was older than that of mild patients, and the median ages of mild and severe patients were 40 and 60 years old, respectively, suggesting that elderly patients were at greater risk of severe COVID-19 [9]. With the increase of age, the compensatory ability of various organs of the organism decreases, in addition, the immune system function and resistance were lower[10, 11]. Therefore, we should focus on strengthening the management of elderly COVID-19 patients. The clinical manifestations of different types of COVID-19 were different. Whether it was mild or severe, fever was the typical symptom, cough and fatigue were manifested in mild patients, yet, severe patients were more prominent in dyspnea. As we all had known, fever was an acute response to the infection of the virus in the organism. When infecting the SARS-cov-2 virus, during which the body's metabolism was vigorous and oxygen consumption was increased. Furthermore, the SARS-cov-2 virus could attribute to an overactive immune response, and the cytokine storm in the lungs blocked the exchange of air (oxygen or carbon dioxide) and blood in the lung tissue, causing dyspnea and even respiratory failure. When the patient suffered from dyspnea or exacerbation suddenly, this might indicate that the patient's condition had not been controlled effectively, and even progressing towards exacerbation. In this study, the CRP level of all patients was elevated, which was considered being related to the systemic acute phase inflammatory response induced by SARS-cov-2 virus. Furthermore, the lymphocyte count and lymphocyte ratio decreased in the severe COVID-19 patients, while the WBC, neutrophil count, neut%, D-dimer, ALT, AST, LDH, BUN levels elevated, there were significant differences between the mild and severe patients. This fully revealed that in various stress events of systemic inflammatory response, the physiological response of inflammatory cells was often characterized by an increase in neutrophil count and a decrease in lymphocyte count [12]. At the same time, with the extension of fever time, the aggravation of hypoxemia, reducing the tolerance of vital organs to hypoxia and lead to the disorder of the internal environment of the organism. The above results indicated that the inflammatory response was aggravated in severe patients, as well as, the liver function and myocardial were damaged, which further suggested that SARS-cov-2 virus could cause multiple organ damage.
The clinical outcomes of COVID-19 were significantly different in different clinical types, and the prognosis might be worse in severe patients. Therefore, the early identification of severe COVID-19 patients was of great value in controlling the incidence of severe diseases, improving the cure rate, and reducing mortality. So, our study analyzed the laboratory indicators of all COVID-19 patients, including NLCR. NLCR defined as peripheral blood neutrophil-lymphocyte count ratio. Neutrophils and lymphocytes were mainly involved in innate and adaptive immunity, respectively. As a combination of them, NLCR was mostly found in the serum of patients with acute inflammation, reflecting the systemic inflammation of the organism and the balance between them. Therefore, NLCR was more sensitive than any of them alone. NLCR was used as a marker to predict the prognosis of pneumonia [13, 14] and the risk of death from bacterial infection [15] had been reported. When NLCR was elevated, it might be associated with a poor clinical prognosis or an increased risk of death. Our study revealed that NLCR, neut%, CAR, CRP, and LDH were better at distinguishing between mild and severe. Furthermore, NLCR was the optimal maker, a cut-off value for NLCR of 6.15 had 87.5% sensitivity and 97.6% specificity for predicting COVID-19 severity. It is essential to dynamic monitoring the serum NLR levels contribute to evaluate the patient's condition and efficacy. NLCR also was a convenient, economical, and easy-to-obtain clinical inflammatory indicator. Therefore, it was recommended that NLCR could be used as an early predictor of COVID-19 severity.
Limitations
In this study, even though NLCR could predict potentially of COVID-19 severity, there were no the existing NLCR reference values with which to confirm the accuracy of a cut-off value. Studies in large patient cohorts were needed. Moreover, some possible confounder might influence on the NLCR, such as hypertension, diabetes, chronic obstructive pulmonary disease, coronary atherosclerotic heart disease.