Diagnostic accuracy of lung ultrasound for SARS-CoV-2: a retrospective cohort study
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Background: As medical infrastructures are strained by SARS-CoV-2, rapid and accurate screening tools are essential. In portions of the world, reverse transcription polymerase chain reaction (RT-PCR) testing remains slow and in limited supply, and computed tomography is expensive, inefficient, and involves exposure to ionizing radiation. Multiple studies evaluating the efficiency of lung point-of-care ultrasound (POCUS) have been published recently, but include relatively small cohorts and often focus on characteristics associated with severe illness rather than screening efficacy. This study utilizes a retrospective cohort to evaluate the test characteristics (sensitivity, specificity, likelihood ratios, predictive values) of lung POCUS in the diagnosis of SARS-CoV-2, and to determine lung score cutoffs that maximize performance for use as a screening tool.
Results: Lung POCUS examinations had sensitivity 86%, specificity 71.6%, NPV 81.7%, and PPV 77.7%. The Lung Ultrasound Score had an area under the curve of 0.84 (95% CI 0.78, 0.90). When including only complete examinations visualizing 12 lung fields, lung POCUS had sensitivity 90.9% and specificity 75.6%, with NPV 87.2% and PPV 82.0% and an area under the curve of 0.89 (95% CI 0.83, 0.96). Lung POCUS was less accurate in patients with a history of interstitial lung disease, severe emphysema, and heart failure.
Conclusions: When applied in the appropriate patient population, lung POCUS is an inexpensive and reliable tool for rapid screening and diagnosis of SARS-CoV-2 in symptomatic patients with influenza-like illness. Adoption of lung POCUS screening for SARS-CoV-2 may identify patients who do not require additional testing and reduce the need for RT-PCR testing in resource-limited environments and during surge periods.
Keywords: COVID-19; Diagnosis; POCUS; RT-PCR; SARS-CoV-2; Triage; Ultrasound.
Conflict of interest statement
GL is an unpaid consultant for EchoNous, an ultrasound device company. EchoNous machines were used for four of the examinations used in the study. EchoNous was not involved in the design, execution, analysis or writing of this work. The other authors have no competing interests.