key: cord-0785920-nookd6af
authors: Bahrami-Motlagh, Hooman; Sanei Taheri, Morteza; Abbasi, Sahar; Haghighimorad, Maryam; Salevatipour, Babak; Alavi Darazam, Ilad
title: Accuracy of Low-Dose Chest CT Scan in Detection of COVID-19
date: 2020-05-27
journal: Radiol Cardiothorac Imaging
DOI: 10.1148/ryct.2020200256
sha: c0e650e70e5e277c34ff403b0e390a2b1f05763e
doc_id: 785920
cord_uid: nookd6af

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I n p r e s s 2 and 93.6%, while in a recent meta-analysis including 63 studies, Kim et al (2) reported combined sensitivity and specificity of chest CT for the diagnosis of COVID -19, considering PCR test as the reference standard, as 94% and 37%, respectively. Pooled prevalence of COVID-19 mainly from reports in China is about 39%, which is near to what Dangis et al (1) report with described pretest probability of 43%. Additionally, we have conducted a study in Tehran, Iran, utilizing low-dose chest CT on 163 patients and observed a sensitivity value of 96.6% (95% CI: 90%, 99%), and specificity value of 36.5% (95% CI: 26%, 49%) (unpublished results), more compatible with the numbers in the mentioned meta-analysis. Although Dangis et al (1) stated that a potential reason for their high specificity was the repeated RT-PCR test after 24 hours in cases with initial negative RT-PCR result, the specificity of standard-dose CT scan in four previous studies with repeated RT-PCR have ranged between 25% and 56% (3) (4) (5) (6) . It seems that other explanations for the observed high specificity of low-dose chest CT should be explored.

Additionally, the specificity of low-dose CT scan for subset of patients with initial negative RT-PCR results are not reported separately in their study.

In conclusion, this remarkable study by Dangis et al (1) demonstrates excellent accuracy of lowdose chest CT in the diagnosis of COVID-19 pneumonia, with exceptional high specificity compared to previous standard-dose studies, which remains to be further validated. Second, there is an inherent trade-off between test sensitivity and specificity. In a situation with limited availability of an imperfect reference test, sensitivity is typically preferred over specificity, and a I n p r e s s 5 low threshold for diagnosis is used. As previous studies reported a very high sensitivity (97% vs 86% in our study), this negatively affected specificity (2, 4) .

Third, our study should not be read as superior performance of low-dose versus standard-dose CT. However, excellent reproducibility and accuracy suggests low dose is sufficient for diagnosis, and radiation exposure should be reduced. We used CareDose4D (Siemens Healthineers) to adapt radiation parameters, including CarekV which selects the optimal tube voltage. New techniques may even further reduce radiation exposure (6) .

Fourth, the prevalence of pneumonia from non-COVID-19 viruses (the most challenging differential diagnosis of COVID-19 on CT) in our cohort was very low, further increasing CT specificity.

In conclusion, differences in study populations and reference tests change the estimated performance of a screening test. Careful consideration of these differences is necessary in order to place research results in a proper clinical context.

Accuracy and reproducibility of low-dose submillisievert chest CT for the diagnosis of COVID-19. Radiol: Cardiothoracic Imaging

Correlation of chest CT and RT-PCR testing in coronavirus disease 2019 (COVID-19) in China: a report of 1014 cases

Diagnostic performance of CT and reverse transcriptase-polymerase chain reaction for coronavirus disease 2019: a meta-analysis

Chest CT features of COVID-19 in

Performance of radiologists in differentiating COVID-19 from viral pneumonia on chest CT

Feasibility of Dose-reduced Chest CT with Photoncounting Detectors: Initial Results in Humans