Thanks to its wide availability, rapid execution, and low cost, chest X-Ray can be considered as a first-line tool in the assessment of lung abnormalities, also in the context of COVID–19 emergency.
The study by Wong et al retrospectively assessed the performance of chest X-Ray in COVID–19 infection, on 64 patients, who executed chest X-rays at baseline and follow-up, for a total of 255 examinations . They observed that consolidation was the most common finding (47%), followed by GGO (33%); chest abnormalities were bilateral in 50% of cases, with a peripheral distribution in 41% of cases and prevalent involvement of the lower zones in 50%. Pleural effusion was found in 3% of patients. They also proposed a radiograph score for a quantification of the consolidation and GGO according to their extension: 0 = no involvement; 1 = <25%; 2 = 25–50%; 3 = 50–75%; 4 = >75% involvement, but in their study the score was assigned by two radiologists in consensus, therefore the inter-observer reliability was not analysed. At baseline, 41% of patients had a severity score of 41%, and no patient had a score > 6.
In their case series, 31% of patients had a normal baseline X-Ray, with reported a sensitivity of 69%, when compared to RT-PCR, and the presence of one patient with falsely negative chest X-Ray, when compared to CT.
In our study, GGO were the most common findings (88%), followed by consolidation (51/110, 46%), and this is in line with the features previously observed on chest CT [10–14].
Pleural effusion was observed in 5/110 (4.5%) of cases.
Chest X-Rays baseline abnormalities showed bilateral involvement in 67/110 (61%), with a prevalent peripheral distribution (48/110; 43.5%), followed by perihilar and peripheral (35/110, 32%) and by perihilar distribution (16/110, 14.5%), and a predilection for the lower zones. Therefore, we confirmed that chest X-Ray findings and distribution are similar to those previously reported for chest CT [10–16].
In our case series, X-Ray showed a high value of sensitivity, higher than the one reported by Wong et al . The possible explanation of this difference has been recently provided by the Fleischner Society : the sensitivity of chest X-Ray is variable according to the community norms and public health directives, in countries where patients are encouraged to present early in the course of their disease, as in China, X-Ray showed limited value, whereas in a context where patients are recommended to stay at home till advanced symptoms, chest X-Ray is generally positive at the time of presentation.
This article also highlighted that the equipment portability is an important advantage of chest X-Ray, which eliminates the risk of COVID–19 transmission along the transport route to the CT scanner and in the CT suite .
A different severity scoring system for chest X-Ray has recently been proposed by Borghesi and Maroldi . The authors proposed a lung division into six zones on frontal chest projection, with attribution of a score based on the types of abnormalities: 0 = no lung abnormalities; 1 = interstitial infiltrates; 2 = interstitial and alveolar infiltrates (interstitial predominance); 3 = interstitial and alveolar infiltrates (alveolar predominance), with a possible maximum global score of 18. This score showed high inter-observer agreement and had significant correlation with the patients ‘outcome, being higher in patients who died than those who were discharged.
The same score was also applied in another study  on 783 Italian patients, and proved to have significant correlation with sex (males had significantly higher scores than females), and age (males aged ≥50 years and females aged ≥ 80 years showed the highest scores).
This study has several limitations. First, in our institution chest CT was not routinely executed in COVID–19 patients, therefore a gold standard imaging was not available for comparison. Second, as we selected only COVID–19 positive patients in our case series, we assumed no false positive or true negative patient was present.
Third, the timing of the baseline X-Ray acquisition in relation to the onset of the symptoms was inhomogeneous, as well as the timing of execution of the follow-up X-Ray, however we can consider that this inhomogeneity is representative of the current clinical situation.
In conclusion, our results support the role of chest X-Ray as a first-line tool in COVID–19 patients’ management, due to its high sensitivity at baseline assessment, in a high pre-test probability environment.
The use of a radiological score can result in clearer communication with Clinicians and a more precise assessment of disease evolution and treatment effects.