The most common clinical symptoms of COVID-19 are fever and cough, with other nonspecific symptoms including shortness of breath, dyspnea, headache, muscle soreness, and fatigue . The latest diagnosis and treatment guidelines state that patients with severe or critical type COVID-19 may present with moderate or low fever, or even without an elevated body temperature . Only 4 patients in this series presented with a body temperature of > 39°C. As the temperature on the day of admission may not reflect recent fluctuations, patients with mild or moderate (i.e., common type) infections may also present with moderate, low, or no fever. About 20% of the reported cases have been severe, and the reported overall mortality is approximately 3% . Our results were in line with that trend, and a severe disease rate of 18.6% indicated that most patients were manageable and treatable. Fortunately, no deaths have occurred in any of the three study groups, which might be a consequence of the few patients with severe disease and comorbidities. Reducing the fatality rate remains a top priority in the current campaign against COVID-19.
The predominant features of COVID-19 pneumonia on CT imaging were bilateral and subpleural GGOs and consolidative pulmonary opacities that were manifestations of lung injury . The autopsy report of the first case of COVID-19 in China noted severe lung injury with gross pathology that was consistent with the distribution of the CT imaging findings. The COVID-19 lesions primarily involved the lungs with little evidence of damage to other organs. Therefore, the overall CT severity scores comprising the sum of the scores of the affected lung lobes can be used to evaluate the degree of lung injury in COVID-19 patients.
In this study, the NLR was higher in patients with severe lung injury than in those with moderate injury, similarly, it was higher in those with moderate injury than in those with mild injury. NLR values were positively correlated with CT severity scores, with the NLR increasing along with the increasing severity of lung injury as shown in Fig. 1-3. This finding indicates that like the CT severity score, NLR was an objective indicator of the severity of lung injury and in line with a recent report of 5 COVID-19 patients with rising neutrophil and falling lymphocyte counts before their death . Lymphocytopenia has been reported in biopsies of patients with COVID-19 and may be a significantly related to disease severity and mortality . The NLR has been identified as an independent risk factor for severe COVID-19 . As it easy to monitor and easier to apply than some other more complex models it may be useful for identifying patients whose prognosis would be improved by early intervention. Positive RT-PCR and negative CT findings or positive CT findings with negative RT-PCR results are both seen in COVID-19 patients [12, 20]. In a large retrospective study, 147 of 308 of patients (48%) with negative RT-PCR results and positive CT findings were reconsidered as highly suspect cases . COVID-19 patients with positive RT-PCR results and negative CT findings have not been extensively studied, but cannot be taken lightly. It is possible that in the early stage of infection the detectable viral load is not sufficient to cause visual pneumonia. Some cases may not progress because of self-limiting infections with a clinical diagnosis of mild type. Other patients may experience infections with visible lesions on follow-up CT scans and progress to common- or severe-type disease . Negative CT findings in patients with PCR-confirmed infections suggests that that chest CT scans are lacking in sensitivity and cannot alone reliably exclude COVID-19, especially in the early stages of infection . We used ROC curve analysis to estimate an optimal NLR cutoff value of 3.634 to differentiate negative and positive CT findings in confirmed COVID-19 patients. If the NLR is > 3.634, we should be alert to the possibility of emerging lung lesions in patients with previous negative CT findings. We believe that NLR has important clinical significance in predicting the severity of either lung injury or illness in COVID-19 patients, and could be a powerful complement to chest CT scans.
If medical resources are lacking, then follow-up CT scans may be available only for patients with evolving disease status under outbreak conditions. Bedside chest radiographs are possible for immobilized or weak patients. Neither is as convenient as routine blood counts, and plain radiographs do not have the high spatial and density resolution provided by chest CT images .
There are several limitations to our study. Firstly, none of the patients were given pulmonary function tests as a baseline reference because of the high risk of infection. Secondly, the clinical and laboratory data were limited during this emergency period as the participating hospitals were fully occupied. Finally, as this was a cross-sectional, retrospective study and we could not evaluate ongoing changes in the NLR and CT images. Longitudinal studies are needed.
In conclusion, the NLR objectively reflected the degree of lung injury and predicted the progress of COVID-19. We recommend giving priority to the economy and convenience of this monitoring method. Clinical use of the NLR may help to alleviate shortages of medical resources during the outbreak in relatively underdeveloped areas and can serve as a novel infection marker in other countries experiencing this COVID-19 pandemic.