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Accuracy of chest CT in the diagnosis of SARS-CoV-2 infection: initial experience in an oncology center

This month, the Revista Radiologia Brasileira (RB) published in Ahead of Print a study of paramount importance for radiologists and the medical and scientific community as a whole.

Entitled “Accuracy of chest CT in the diagnosis of SARS-CoV-2 infection: initial experience in an oncology center”, the study, conducted by doctors Paula Nicole Vieira Pinto Barbosa, Almir Galvão Vieira Bitencourt, Gabriel Diaz de Miranda, Maria Fernanda Arruda Almeida and Rubens Chojniak, aimed to assess the accuracy of chest computed tomography (CT) in patients with suspected infection by SARS-CoV-2 at an oncology center.

This is a retrospective, single-center study that selected 91 patients who underwent chest CT and RT-PCR testing on the same day. CT results were classified as negative, typical, indeterminate or atypical findings. Diagnostic accuracy, sensitivity and specificity were calculated for two scenarios: in the first, only CT with typical findings was considered positive. In the second, typical or indeterminate findings were considered positive.

Check below a brief interview with the authors about the article that, in addition to the version in ahead of print, will be available in the next issue of RB.

How was this study done?

We compared the results of CT scans with the results of the PCR test in consecutive symptomatic patients seen at the hospital with suspected Covid-19.

The CT and PCR exams were performed on the same day and the findings of the CT exams were classified according to international guidelines already published, according to the suspicion for Covid-19.

We then analyzed the accuracy of the CT for the presence of Covid-19 using two interpretation criteria: in one of them, we considered positive for Covid-19 only the CTs that presented findings already described as typical, in this interpretation scenario we verified a high specificity of the test and a lower rate of false positive results. And, in the other interpretation criterion, we considered CT exams positive for typical or indeterminate findings for Covid-19. In this scenario, we verified a high sensitivity of the CT and a low rate of false-negative results.

What is the contribution of this study?

As CRP tests are scarce and their results take time to come out, we found that CT can help with screening in this group of symptomatic patients. The result of the CT examination separates two groups, one with high and one with low chance of infection by Covid-19 and, thus, can assist in decisions that need to be made before the result of the PCR test.

An interesting aspect in the analysis of the results is that we know that the PCR test also has its limitations, and that negative results are not uncommon in patients with Covid-19. Therefore, the performance of CT may be even better than that estimated by studies that use PCR as a reference standard, as in our work. Some studies suggest that CT may have a higher sensitivity than the CRP test in certain clinical contexts / populations.

How can we adopt this information in practice in our environment?

In a context of limited resources and structure where PCR tests may be lacking, the result of the PCR test takes time to come out, isolation units and ICU beds are lacking, as we have already seen in some places in Brazil, it is necessary to make decisions without the result of the PCR test. Who are we going to test? Who are we going to hospitalize, isolate, or hospitalize in an ICU bed until the result of the PCR test comes out?

The CT Result, despite not having the ideal accuracy for a Covid-19 diagnostic test and not being able to directly verify the presence of the virus, has sufficient performance to help in the screening, in the decision of resource allocation, particularly in the criterion of greater specificity considering only typical findings. Prioritizing the use of resources for patients with high probability for the disease.

The other interpretation criterion, which also considers the indeterminate findings is more sensitive, will not lose many infected patients, however, it tends to demand resources for a greater number of patients due to the high rate of false positive results.

We realized that this is a way of using CT that was already occurring in practice in some centers and for some patients.

Is this usage profile being adopted by international companies?

Most international societies have not been recommending CT as a systematic diagnostic test, or screening for all patients with suspected Covid-19. But this is due to the recognition that false-positive and negative results are not uncommon. Other viruses and pathologies may have similar findings to Covid-19 and, especially at the beginning of the symptomatic infection, CT may not show pulmonary changes. However, in the scenario in which we are suggesting the indication of CT as a screening test, it is not a conventional situation with wide access to diagnostic and treatment resources. This approach has been used by Chinese health authorities and the consensus on the use of imaging methods for the management of Covid-19, recently published by the Fleischner Society, a renowned international thoracic radiology society, has now started to predict the type of application of the CT during the pandemic. We believe that with the accumulation of experience and information, this approach should be considered in situations of scarcity of resources.

RESULTS

The mean age of the patients was 58.2 years, the majority being men (60.4%) and with a history of previous cancer (85.7%).

CT demonstrated typical findings in 28.6%, indeterminate in 24.2% and atypical in 26.4%.

RT-PCR results were positive for SARS-CoV-2 at 27.5%.

Sensitivity, specificity and accuracy in the first and second scenarios were, respectively, 64.0%, 84.8% and 79.11T1T, and 92.0%, 62.11T1T1 and 70.3%.

CONCLUSION

CT is highly accurate for the diagnosis of SARS-CoV-2 infection. Different interpretation criteria provide greater sensitivity or specificity. CT should be integrated as a screening test in environments with limited resources during the pandemic, to help optimize the use of PCR tests, isolation beds and intensive care units.

RB is the official scientific publication of the Brazilian College of Radiology and Diagnostic Imaging (CBR) and is part of the group of journals indexed to SciELO (Scientific Electronic Library Online), LILACS (Latin American and Caribbean Literature of Information in Sciences of the Health), SCOPUS and PUBMED CENTRAL.

Read the article: http://www.rb.org.br/detalhe_aop.asp?id=3269

Also available through the CBR Digital Library App (Android and iOs)

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