Pairing Chest CT and CO-RADS Gives “Rapid Test Result” for Some COVID-19 Patients

Using the COVID-19 reporting and data system (CO-RADS) to analyze and interpret chest CT scans can provide a quick, accurate diagnosis for patients who have exhibited symptoms of the virus for longer than 48 hours, a new study has found.

In an article published in the Nov. 17 Radiology, a multi-institutional team of researchers from The Netherlands set out to determine whether – in a real-life scenario – chest CT scans can be used to help providers make faster, reliable COVID-19 diagnoses. Knowing whether this is possible could be particularly helpful as the number of positive cases continues on a steep rise and the world enters the second wave of the pandemic.

“Clinicians need rapid and reliable diagnosis of coronavirus disease 2019 (COVID-19) for proper risk stratification, isolation strategies, and treatment decisions,” said the team led by Steven Schalekamp, M.D., Ph.D., from the department of radiology, nuclear medicine, and anatomy at Radboud University Medical Center in Nijmegen, The Netherlands.

Example chest CT scans of patients with a true positive (case 1) and false positive (case 2) CO-RADS 4 score. (case 1). True positive CO-RADS 4 chest CT: (a,b) two axial slices and (c) a coronal slice of a 79-year-old female with 9 days of symptoms. CT shows diffuse ground-glass opacities close to visceral pleural surfaces but superimposed on emphysematous changes. Also note the widened esophagus. Coronavirus disease 2019 was RT-PCR confirmed. (case 2) False positive CO-RADS 4 chest CT: (d,e) two axial slices and (f) a coronal slice of a 51- year-old female with 2 days of symptoms. CT shows bilateral multifocal areas of consolidation with halo and subtle areas of ground glass without contact to visceral pleural surfaces. RT-PCR for SARS-CoV2 was repeatedly negative and an alternative diagnosis was established with a blood culture confirmed line sepsis. Courtesy: RSNA

Based on the analysis of their retrospective multi-center study, the team found that positive chest CT interpretation shows high performance for COVID-19 pneumonia diagnosis with an odd-ratio of 25.9. To reach this conclusion, they enrolled 1,070 patients with moderate-to-severe upper respiratory symptoms who presented to one of six emergency departments between March 2020 and April 2020. Of that group, 536 (50 percent) had positive RT-PCR tests, and another 137 (13 percent) were considered as potential positive cases.

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The team also examined clinical symptoms in concert with CT findings and determined they gave some indication of infection, the team said – 67 percent of people who had symptoms for less than 48 hours also had pulmonary findings on CT. The same was true for 95 percent of patients with symptoms lasting longer than two days. Because RT-PCR sensitivity drops off after seven days of symptoms, CT can be vital to diagnosing those patients, the team said.

When scored using CO-RADS, 235 CT scans (22 percent) were CO-RADS 1, 140 (13 percent) were CO-RADS 2, 134 (13 percent) were CO-RADS 3, 120 (11 percent) were CO-RADS 4, and 441 (41 percent) were CO-RADS 5. When compared to RT-PCR, for scores of 4 or more, the team determined the sensitivity was 86 percent, and the specificity was 81 percent, leading to the 25.9 odds ratio. In addition, using a clinical reference standard for the same scores, sensitivity was 77 percent, and specificity was 90 percent with an odds ratio for COVID-19 diagnosis of 30.6. These results, they said, point to the potentially critical use of chest CT and CO-RADS.

“Chest CT exams interpreted using the CO-RADS system allow for a rapid test result in the emergency department of patient with suspected COVID-19 pneumonia,” they said. “This suggests a potential role for chest CT in helping to optimize risk stratification and isolation strategies of patients urgently presenting for hospital care during the first and second wave of this pandemic.”

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Being able to use CT scans for diagnosing patients could also help providers and facilities address many of the issues that erupted during the initial wave of the pandemic. Workflow, isolation, personal protective equipment, and treatment decisions were all impacted, the team said, and being able to process patients faster could help alleviate these stresses.

Although the role that chest CT can play in COVID-19 diagnosis is still evolving, in an accompanying editorial, by Brett M. Elicker, M.D., clinical professor of radiology and biomedical imaging at the University of California, San Francisco, said these results do indicate there are several ways CT can be useful with detecting and managing patients positive for infection.

Not only can CT be used to identify alternative or superimposed causes behind pulmonary symptoms, such as bacterial infection or pulmonary embolism, but it can also influence therapy decisions, identifying which patients could most benefit from active treatment. The scan can also be paired with RT-PCR to identify which patients should be isolated, and, in resource-limited areas where RT-PCR tests may not be available or test results are slow or inaccurate, CT can be used for diagnosis, he said.

Overall, he said, Schalekamp’s team revealed the significant role CT can play in evaluating patients who might have COVID-19 in comparison to both RT-PCR and a clinical reference standard.

“The results of this study…can form a foundation for other investigations whose goal is to further elucidate the potential roles of CT in the detection and characterization of this deadly disease,” Elicker said.

Although the study had limitations, including less-than-optimal training for radiologists with CO-RADS at the time of the study and the possibility that the findings might not be reproducible in a lower-incidence setting, these results do still carry potential importance, the team said.

“Our study may indicate that employing CO-RADS improves CT performance in diagnosis of COVID-19 in clinical practice,” the team said. “Our study showed that CT can be a useful risk stratification tool for COVID-19: which may be advantageous…to counteract emergency department crowding.”

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