How likely is a patient with COVID-19-like symptoms and hypoxia but negative chest X-ray (CXR) to have COVID-19?Posted on by
- CXR or CT are not recommended to diagnose COVID-19 as viral PCR is the only specific method of diagnosis. A normal chest image cannot exclude the diagnosis of COVID-19 especially if patients have had a recent onset of symptoms.
- Greatest lung abnormalities have been found on CT 10 days after the initial onset of symptoms.
- Routine use of imaging for screening, diagnosis, and surveillance of COVID-19 is not recommended. It is recommended for confirmed patients who may have developed complications from COVID-19 or in the emergency room setting.
- The value of the image must outweigh the risk of radiation exposure and COVID-19 transmission, and the use of PPE, cleaning time and downtime. Imaging should be limited to patients in whom the results are expected to change management.
I. ROLE OF IMAGING IN DIAGNOSIS OF COVID-19
- The Canadian Society of Thoracic Radiologists (CSTR) and Canadian Association of Radiologists (CAR) stated that a normal chest CT cannot exclude diagnosis of COVID-19 especially for patients with recent onset of symptoms. It lacks sensitivity (69%). (1)
- The CDC does not currently recommend CXR or CT to diagnose COVID-19. Viral PCR is the only specific method of diagnosis. (2)
- A study of the frequency of CXR findings in positive covid patients found baseline CXR to have a sensitivity of 69%. Of the 64 patients in the study, 51 (80%) showed abnormalities on CXR at some point. The severity of CXR findings peaked at 10-12 days from the date of symptom onset. (3)
- A study of the clinical features of COVID-19 reported no CXR or CT abnormalities in 17.9% of patients with nonsevere disease and 2.9% with severe disease. Severe disease includes symptoms of dyspnea, hypoxia, or >50% lung imaging on involvement. (4)
- The findings on chest imaging in COVID-19 are not specific and overlap with other infections (eg. H1N1, influenza, SARS, MERS). (2)
II. COVID-19 IMAGING TIMING
- CXR is often normal in early disease (1).
- Patients that were evaluated by CT throughout the course of the disease showed greatest lung abnormalities 10 days after the initial onset of symptoms. (5, 2)
III. USE OF IMAGING DURING THE COVID PANDEMIC
- The value of the image must outweigh the risk of radiation exposure, risk of COVID-19 transmission, consumption of PPE, and the need for cleaning and downtime of radiology rooms. Imagining should be limited to patients in whom the results are expected to change management. (1, 6)
- The CSTR/CAR recommends against the use of routine CT for screening, diagnosis, and surveillance of COVID-19. It is recommended for confirmed patients who may have developed complications. (1)
- Imaging may also be helpful in the ED when the RT-PCR assay is not yet available. If positive, the pre-test probability of a diagnosis of COVID-19 will rise. The imaging may also suggest an alternative diagnosis that requires treatment (1)
- Imaging is indicated in a patient with COVID-19 with worsening respiratory condition and, if resources are constrained, for medical triage of suspected COVID-19 cases with moderate-severe clinical features and a high pre-test probability of disease. (6)
Flowchart for COVID-19 chest imaging (1)
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- Canadian Association of Radiologists. Canadian Society of Thoracic Radiology and Canadian Association of Radiologists’ statement regarding chest imaging in suspected and confirmed COVID-19 [Internet; cited 2020 May 12]. Available from: https://journals.sagepub.com/doi/10.1177/0846537120924606
- American College of Radiology. ACR recommendations for the use of chest radiography and computed tomography (CT) for suspected COVID-19 infection [Internet; cited 2020 April 8]. Available from: https://www.acr.org/Advocacy-and-Economics/ACR-Position-Statements/Recommendations-for-Chest-Radiography-and-CT-for-Suspected-COVID19-Infection
- Wong, H.Y.F., Lam, H.Y.S., Fong, A.H., Leung, S.T. . Frequency and distribution of chest radiographic findings in COVID-19 positive patients. Radiology [Internet]. 2020 Mar 27 [cited 2020 April 8]. Available from: https://pubs.rsna.org/doi/10.1148/radiol.2020201160
- Guan, W., Ni, Z., Hu, Y., Liang, W., Ou, C., He, J., et al. Clinical characteristics of coronavirus disease 2019 in China. The New England Journal of Medicine [Internet]. 2020 Feb 28 [cited 2020 April 8]. Available from: https://www.nejm.org/doi/full/10.1056/NEJMoa2002032
- Pan, F., Ye, T., Sun, P., Gui, S., Liang, B., et al. Time course of lung changes on chest CT during recovery from 2019 novel coronavirus (COVID-19) pneumonia. Radiology [Internet, cited 2020 April 8]. Available from: https://pubs.rsna.org/doi/10.1148/radiol.2020200370
- Rubin, G.D., Ryerson, C.J., Haramati, L.B., Sverzellati, N., Kanne, J.P., Raoof, S., et al. The role of chest imaging in patient management during the COVID-19 pandemic: a multinational consensus statement from the Fleischner Society. Radiology [Internet, cited 202 April 8]. Available from: https://pubmed.ncbi.nlm.nih.gov/32255413/?from_term=CXR+covid&from_pos=2
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