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Chest X-ray and CT Scan for COVID-19

COVID-19, the disease caused by SARS-CoV-2 (a new type of coronavirus), continues its spread throughout the United States. While COVID-19 test kits have been in limited supply, new studies from China suggest chest radiographs (X-rays) and chest computed tomography (CT) scans can help diagnose the disease. Both can reveal abnormalities indicative of lung disease, including COVID-19.

Currently, the Centers for Disease Control and Prevention (CDC) and the American College of Radiology do not recommend chest X-ray or CT for the screening or diagnosis of COVID-19. Viral throat swab testing is the only specific test for the disease, and is necessary to confirm any infection suspected on the basis of imaging findings.

X-ray

A chest X-ray (radiograph) is the most commonly ordered imaging study for patients with respiratory complaints. In the early stages of COVID-19, a chest X-ray may be read as normal. But in patients with severe disease, their X-ray readings may resemble pneumonia or acute respiratory distress syndrome (ARDS).

Importantly, these findings are not specific for COVID-19 disease, and may overlap with those of other infections. Doctors cannot make a confident diagnosis of COVID-19 disease on the basis of chest X-ray alone.

X-ray of confirmed COVID-19 patient
X-ray of confirmed COVID-19 patient. Courtesy of Dr. Fabio Macori, Radiopaedia.org

Chest X-ray findings of COVID-19 disease include:

  • Bilateral multifocal consolidations that may progress to involve entire lungs: The term "consolidation" refers to the filling of pulmonary airspaces with fluid or other products of inflammation. The phrase "bilateral multifocal" means that the abnormalities occur in different locations in both lungs.
  • Small pleural effusions: This is abnormal fluid that develops in the spaces around the lungs.

CT Scan

Also referred to as a CAT scan, a CT scan of the chest is a specialized type of imaging study which uses X-rays to create 3D images of the chest. Chest CT is more effective than chest X-ray in the detection of early COVID-19 disease.

However, up to 50% of patients may have a normal chest CT within the first two days after the onset of symptoms. Also, other types of pneumonia may mimic COVID-19 on chest CT.

Nevertheless, suspicious findings on chest CT are a valuable clue (along with the clinical presentation and exposure history) that a patient may have COVID-19.

The severity of COVID-19 varies significantly from person to person. Chest CT may also be used as an initial tool to assess disease severity, as well as to monitor for progression or resolution of disease.

CT scans of confirmed COVID-19 patients
CT scans of confirmed COVID-19 patients. Left: Courtesy of Dr. Domenico Nicoletti. Right: Courtesy of Dr. Bahman Rasuli. Radiopaedia.org. 

Chest CT findings of COVID-19 disease include:

  • Multifocal ground-glass opacities and consolidations: The term "ground-glass opacity" refers to the hazy appearance of the lungs on imaging studies, almost as if sections are obscured by ground glass. It may be due to the filling of pulmonary airspaces with fluid, the collapse of the airspaces, or both.
  • Location: Abnormalities tend to occur in the peripheral and basal areas of the lungs, more commonly in the posterior lung bases.

CT Scan and Swab Test

The most reliable test for the diagnosis of SARS-CoV-2 infection is an oropharyngeal or nasopharyngeal polymerase chain reaction (PCR) assay, involving a throat swab or a swab of the place where back of the nose meets the throat.

In this test, a sample is collected from the back of the nose or throat and tested for viral RNA. There are very few false positives with this test. However, some reports have suggested a sensitivity of 60-70%, meaning that there may be a significant number of infected people who actually have a negative test.

Multiple tests are unlikely to be done if the first test is negative, but if a patient's condition gets worse, a second test may be done to confidently rule out infection.

Some reports from China have suggested that, in some patients with COVID-19 pneumonia, abnormalities on chest CT may appear despite negative swab tests. This, combined with the initial lack of sufficient test kits, has led some medical practices to request chest CTs to screen patients for the disease.

Doctors should be very careful about this approach. Remember that chest CT may look normal in patients with early disease. Also, the CT abnormalities of COVID-19 may appear similar to those of other infections.

We must also be sensitive to the fact that imaging tests require patients to travel to a radiology department and interact with other patients and medical personnel. Injudicious use of medical imaging may needlessly expose others to coronavirus infection.

A chest CT may be helpful if used carefully in sick, hospitalized patients, as it may be useful to gauge the severity and progression of the disease. But neither CTs or X-rays are currently recommended to diagnose COVID-19.

A Word From Verywell

As the world reels from the COVID-19 pandemic, public health authorities must comb through the newest and most reliable data to set policies that limit mortality, curtail disease transmission, protect health care workers, and allow the continued function of the health care system.

The available data changes rapidly as the scientific community learns more about the novel coronavirus. No one is comfortable with uncertainty. It is best to follow the recommendations set by groups like the CDC, whose guidelines are supported by the most solid available evidence.

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Article Sources
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  1. American College of Radiology. ACR Recommendations for the use of chest radiography and computed tomography (CT) for suspected COVID-19 infection. Updated March 22, 2020.

  2. Zu ZY Jiang MD, Xu PP, et al. Coronavirus disease 2019 (COVID-19): A perspective from China. Radiology. 2020;200490. doi:10.1148/radiol.2020200490

  3. Kanne JP, Little BP, Chung JH, Elicker BM, Ketai LH. Essentials for radiologists on COVID-19: An update- scientific expert panel. Radiology. 2020;200527. doi:10.1148/radiol.2020200527

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