Computed Tomography (CT): The Most Effective Method for Diagnosing COVID-19

In a study involving more than 1000 patients and published in Radiology, chest computed tomography (CT) was reported to perform better than laboratory tests in diagnosing the novel coronavirus disease (COVID-19). The researchers concluded that, rather than PCR and blood tests, CT should be used as the primary screening tool for COVID-19.

In the absence of drugs or vaccines specific to COVID-19, it is important to detect the disease at an early stage and immediately isolate an infected patient from healthy people.

According to the latest guidelines from China, a diagnosis of COVID-19 should be confirmed by reverse transcription polymerase chain reaction (RT-PCR) or gene sequencing of respiratory or blood samples as a key indicator for hospital admission. However, both practical difficulties and the dynamics of kit production limit the performance of these laboratory tests; for example, the positivity rate for PCR on the first attempt in suspected cases has been reported to be between 30% and 60%.

The low sensitivity of PCR means that many COVID-19 patients may not receive prompt and appropriate treatment. In addition, given the highly contagious nature of the virus, this increases the risk of transmission to a larger population.

Early diagnosis of COVID-19 is very important for treatment and control of the disease. Compared with PCR, thoracic (chest) CT imaging may be a more reliable, practical and rapid method for diagnosing and assessing COVID-19, particularly in the outbreak area.

Chest CT, a routine imaging tool for diagnosing pneumonia, is quick and relatively easy. Recent research has found that the sensitivity of CT for COVID-19 infection, meaning its ability to identify people who are ill, is 98%. For PCR, this figure is 71%.

For the current study, researchers at Tongji Hospital in Wuhan, China set out to investigate the diagnostic value and consistency of chest CT imaging compared with PCR testing in COVID-19.

The study included 1014 patients who underwent both chest CT and PCR testing between January 6 and February 6, 2020. Using PCR testing as the reference, the performance of both tests in diagnosing COVID-19 was assessed. For patients who underwent multiple / serial PCR tests, the dynamic changes in PCR results (from negative to positive and from positive to negative, respectively) were analyzed in comparison with serial CT scans.

The results showed that 601 patients (59%) had positive PCR results and 888 (88%) had positive chest CT scans. The sensitivity of chest CT in suggesting COVID-19 was 97%, based on positive PCR results. Among patients with negative PCR results, 75% (308 of 413 patients) had positive chest CT findings. The interval between the initial negative and positive PCR results was 4 to 8 days.

Approximately 81% of patients who had negative PCR results but positive chest CT scans were subsequently reclassified as COVID-19 cases following a comprehensive analysis of clinical symptoms, typical CT findings and dynamic CT follow-up.

In conclusion, computed tomography (CT) emerges as a more accurate tool than laboratory tests for diagnosing COVID-19. We therefore believe that a CT result should be sufficient for a patient to receive a COVID-19 diagnosis and that serial laboratory and imaging tests should be performed in people with clinical suspicion despite negative test results. However, it must be remembered that rooms where CT scans are performed carry a risk of transmission because of frequent scanning and need to be properly sterilized. 

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