Conflicts with US Guidelines

The Coronavirus Crisis: Is CT More Effective than Laboratory Testing in Detecting COVID-19?

Could it be that we are barking up the wrong tree in terms of how best to diagnose 2019 novel coronavirus COVID-19? Current U.S. guidelines prioritize laboratory testing over computed tomography (CT) and other types of chest scans to detect COVID-19. However, a recent study from Wuhan, China, ground zero for the pandemic, concludes that CT scans are better at diagnosing COVID-19 and should supplant laboratory testing as the primary method of COVID-19 screening.

The Diagnostic Challenge

Current laboratory tests for diagnosis of COVID-19 are based on reverse-transcription polymerase chain reaction (RT-PCR) technology involving the application of gene sequencing for qualitative detection of the SARS-CoV-2 virus that causes the disease from nasopharyngeal and oropharyngeal swab samples of patients showing symptoms or suspected of having coronavirus.

However, there are a number of problems with RT-PCR technology, including its low sensitivity which impairs its effectiveness in detecting the virus. As a result, while a positive test is a reliable indication of infection, a negative test is not a conclusive indication that a patient does not have it. Accordingly, the CDC and US Food and Drug Administration (FDA) are advising physicians not to rule out COVID-19 infection on the basis of a negative test alone but to do so only after evaluating other factors, including clinical observations, the patient’s medical history and epidemiological information.

CT scans, by contrast, are not subject to these same limitations. A CT scan allows doctors to see inside the body. Using a combination of X-rays and a computer to create pictures of organs, bones, and other tissues, it provides much more detail than a regular X-ray. This, coupled with the fact it is fast and relatively easy to perform, make chest CT, a routine imaging tool for pneumonia diagnosis.

The question then becomes: Do these same qualities make chest CT a better method for diagnosing COVID-19?

The Wuhan Study

With this question in mind, researchers at Tongji Hospital in Wuhan, China, set out to investigate the diagnostic value and consistency of chest CT imaging in comparison to RT-PCR assay in COVID-19 detection. They evaluated 1,014 patients who underwent both chest CT and RT-PCR tests between January 6 and February 6, 2020.

The study, which was published in the journal Radiology, found that the sensitivity of CT for COVID-19 infection was 98%, compared to 71% sensitivity of RT-PCR. Specifically, the study results showed that:

  • 601 patients (59%) had positive RT-PCR results;
  • 888 patients (88%) had positive chest CT scans;
  • The sensitivity of chest CT in suggesting COVID-19 was 97%, based on positive RT-PCR results;
  • Among patients with negative RT-PCR results, 75% (308 of 413 patients) had positive chest CT findings; and
  • Of the patients with negative RT-PCR results that had positive CT chest findings, 48% were considered as highly likely cases and 33% as probable cases.

After conducting analysis serial RT-PCR assays and CT scans, the researchers found that the interval between the initial negative to positive RT-PCR results was four to eight days. And of course, 96 hours of not being in isolation or quarantine despite having the virus would be ample time to infect other people.

Bottom Line: Based on these findings, the researchers concluded that CT rather RT-PCR laboratory tests should be used as the primary screening tool for COVID-19. “Early diagnosis of COVID-19 is crucial for disease treatment and control,” the researchers wrote. “Compared to RT-PCR, chest CT imaging may be a more reliable, practical and rapid method to diagnose and assess COVID-19, especially in the epidemic area.”

Conflict with COVID Diagnostic Recommendations in the US

As of March 19, 2020, some medical practices are actually using chest CT to inform decisions on whether to test a patient for COVID-19; but they are doing so only as an interim measure until more widespread COVID-19 laboratory testing becomes available. The Wuhan study’s conclusion that CT be the primary method of COVID-19 detection conflicts directly with current U.S. medical guidelines, including those from the Centers for Disease Control and Prevention (CDC) and the American College of Radiology (ACR), neither of which recommends that CT scan be used as the primary screening or detection method for COVID-19.

Both organizations question the reliability of CT. According to the CDC, a normal chest CT does not mean a person does not have COVID-19 infection and should not dissuade a patient from being quarantined; similarly, an abnormal CT is not specific for diagnosis. Another problem with use of CT scans for COVID-19 detection is that it exposes testers and subsequent patients who get scans in the same location or via use of the same equipment to infection risk.

Accordingly, the CDC has declined to endorse CT or chest radiographs (CXR) to diagnose COVID-19, and maintains that viral laboratory testing remains the only specific method of diagnosis. Even when radiologic findings are suggestive of COVID-19, the CDC requires that they be confirmed via viral testing.

The ACR also recommends not using CT to screen for or as a first-line test to diagnose COVID-19. Specifically, the organization says that:

  • CT should be used sparingly and reserved for hospitalized, symptomatic patients with specific clinical indications for CT and that appropriate infection control procedures be followed before scanning subsequent patients;
  • Facilities may consider deploying portable radiography units in ambulatory care facilities for use when CXRs are considered medically necessary to the extent the surfaces of these machines can be easily cleaned, avoiding the need to bring patients into radiography rooms; and
  • Radiologists should familiarize themselves with the CT appearance of COVID-19 infection so as to be capable of identifying findings consistent with infection in patients imaged for other reasons.


 The clinical basis of the U.S. COVID-19 response is that laboratory testing, while flawed, remains the safest and most reliable method of detecting the disease. However, it is food for thought that empirical experience from Wuhan, China, directly challenges that premise and suggests that another diagnostic method, namely CT and chest scans, may be much more effective in determining whether a patient has or does not have COVID-19. 




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