Chest CT Effective as First-Line COVID-19 Diagnosis Tool

September 2, 2020

Findings from a French study contradict recommendations from the American College of Radiology and the international community against using chest CT scans an initial tool for viral diagnosis.

In an about-face to the current guidelines on the use of chest CT for COVID-19 diagnosis, a group of investigators from France published a study this week that supports the use of the scan for initial diagnosis of viral infection.

Even though guidance from the American College of Radiology and other international groups have recommended against using chest CT as a first-line diagnostic tool and using reverse transcription polymerase chain reaction (RT-PCR) instead, this article, published Sept. 1 in Radiology, challenges that recommendation. Instead, according to the group led by Guillaume Herpe, M.D., Ph.D., from University Hospital Center Poiters, chest CT can be successfully used for initial diagnosis and triage of patients with suspected COVID-19.

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“In the context of this epidemic, the low sensitivity of RT-PCR implies that many patients with COVID-19 may not be identified and, consequently, may not be isolated from healthy population,” the team wrote. “Chest CT can detect some characteristic features in almost all patients with COVID-19 pneumonia.”

These features captured by chest CT have also appeared in patients with clinical symptoms who received negative RT-PCR results, they said.

Despite being considered the gold standard for detection, RT-PCR has several disadvantages. In addition to having performance differences based on manufacturer, patient viral load, and potential improper sampling, one of the biggest concerns with this test is timing. In many cases, results can be delayed for hours – a critical problem when providers are waiting for a diagnosis to determine treatment and control exposure.

“It is essential to detect this disease at its earliest stage and immediately isolate the infected person to limit its spread,” the team asserted.

To reach this determination about chest CT, Herpe’s team conducted a CT scan survey from 26 hospital radiology departments throughout France from March 2, 2020, and April 24, 2020 – dates that marked the peak of the pandemic in that country. The departments were instructed to included details on all asymptomatic patients who were suspected of COVID-19 infection and who underwent both chest CT and RT-PCR within a 48-hour period.

COVID-19 Diagnostic Performance for Chest CT and RT-PCR

MeasureInitial CTInitial RT-PCR
Sensitivity9087
Specificity9199
Positive Predictive Value9299
Negative Predictive Value8987
Accuracy9097

From that survey, they gathered CT scans and RT-PCR results from 4,824 patients, 2,564 (53 percent) of whom tested positive for COVID-19. Based on the patient’s final diagnosis from the hospital discharge report, the sensitivity and specificity of the chest CT scans were 90 percent and 91 percent, respectively. In particular, the team determined that 90 percent of 103 patients who initially had positive CT results but a negative RT-PCR test eventually received positive RT-PCR results on a re-test. 

The test also determined the negative predictive value at final diagnosis for patients with both negative chest CT and RT-PCR was 99 percent – 2,035 out of 2,050 patients.

Based on these results, the team said, their findings stand in stark contrast to the original recommendations around the use of chest CT for initial diagnosis during the COVID-19 pandemic. Consequently, they should be considered as part of clinical decision-making.

“The results of [our] survey shed light on the role of chest CT in the current COVID-19 pandemic as an initial diagnostic tool in areas of relatively high disease prevalence,” they wrote. “These data need to be considered during planning for either local hospital or national budget cycle.”