COVID-19 Evidence Alerts
from McMaster PLUSTM

Current best evidence for clinical care (more info)

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Diagnosis Borakati A, Perera A, Johnson J, et al. Diagnostic accuracy of X-ray versus CT in COVID-19: a propensity-matched database study. BMJ Open. 2020 Nov 6;10(11):e042946. doi: 10.1136/bmjopen-2020-042946.

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.

Discipline / Specialty Area Score
Hospital Doctor/Hospitalists
Internal Medicine
Infectious Disease
Emergency Medicine
Comments from MORE raters

Emergency Medicine rater

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.

Emergency Medicine rater

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.

Respirology/Pulmonology rater

It is a methodologically coherent study, which provides evidence on a known fact.

Respirology/Pulmonology rater

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.