Current best evidence for clinical care (more info)
OBJECTIVES: To identify the diagnostic accuracy of common imaging modalities, chest X-ray (CXR) and CT, for diagnosis of COVID-19 in the general emergency population in the UK and to find the association between imaging features and outcomes in these patients.
DESIGN: Retrospective analysis of electronic patient records.
SETTING: Tertiary academic health science centre and designated centre for high consequence infectious diseases in London, UK.
PARTICIPANTS: 1198 patients who attended the emergency department with paired reverse transcriptase PCR (RT-PCR) swabs for SARS-CoV-2 and CXR between 16 March and 16 April 2020.
MAIN OUTCOME MEASURES: Sensitivity and specificity of CXR and CT for diagnosis of COVID-19 using the British Society of Thoracic Imaging reporting templates. Reference standard was any RT-PCR positive naso-oropharyngeal swab within 30 days of attendance. ORs of CXR in association with vital signs, laboratory values and 30-day outcomes were calculated.
RESULTS: Sensitivity and specificity of CXR for COVID-19 diagnosis were 0.56 (95% CI 0.51 to 0.60) and 0.60 (95% CI 0.54 to 0.65), respectively. For CT scans, these were 0.85 (95% CI 0.79 to 0.90) and 0.50 (95% CI 0.41 to 0.60), respectively. This gave a statistically significant mean increase in sensitivity with CT of 29% (95% CI 19% to 38%, p<0.0001) compared with CXR. Specificity was not significantly different between the two modalities.CXR findings were not statistically significantly or clinically meaningfully associated with vital signs, laboratory parameters or 30-day outcomes.
CONCLUSIONS: CT has substantially improved diagnostic performance over CXR in COVID-19. CT should be strongly considered in the initial assessment for suspected COVID-19. This gives potential for increased sensitivity and considerably faster turnaround time, where capacity allows and balanced against excess radiation exposure risk.
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The radiological outcomes in this study did not appear to have much correlation with clinical parameters suggesting COVID-19 severity. This is not relevant to infected patients without respiratory disease. While Dx is faster than RT-PCR, the study was done before the availability of rapid antigen tests and as a result, the study has less relevance today in the rapidly evolving improvement in diagnostics for COVID-19.
While there is a statistically significant difference in favour of CT over CXR; the cost, delays and radiation risks of changing to CT make the recommendation to use CT invalid. There is no difference in outcomes, so unless you are talking in-patients, this recommendation should be ignored.
It is a methodologically coherent study, which provides evidence on a known fact.
Formal study confirms what has been reported in case reports and series. CT is far more sensitive than CXR in demonstrating infiltrates consistent with Covid-19. However, cost, radiation exposure, and down time after each scan, to have adequate room air exchange, make this impractical. Rapid turn around of PCR results for Covid-19 is far more useful.