Chest CT accuracy in diagnosing COVID-19 during the peak of the Italian epidemic: A retrospective correlation with RT-PCR testing and analysis of discordant cases

Abstract

Objectives: The goal of this study was to assess chest computed tomography (CT) diagnostic accuracy in clinical practice using RT-PCR as standard of reference.

Methods: From March 4th to April 9th 2020, during the peak of the Italian COVID-19 epidemic, we enrolled a series of 773 patients that performed both non-contrast chest CT and RT-PCR with a time interval no longer than a week due to suspected SARS-CoV-2 infection. The diagnostic performance of CT was evaluated according to sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and diagnostic accuracy, considering RT-PCR as the reference standard. An analysis on the patients with discrepant CT scan and RT-PCR result and on the patient with both negative tests was performed.

Results: RT-PCR testing showed an overall positive rate of 59.8 %. CT sensitivity, specificity, PPV, NPV, and accuracy for SARS-CoV-2 infection were 90.7 % [95 % IC, 87.7%-93.2%], 78.8 % [95 % IC, 73.8-83.2%], 86.4 % [95 % IC, 76.1 %-88.9 %], 85.1 % [95 % IC, 81.0 %-88.4] and 85.9 % [95 % IC 83.2-88.3%], respectively. Twenty-five/66 (37.6 %) patients with positive CT and negative RT-PCR results and 12/245 (4.9 %) patients with both negative tests were nevertheless judged as positive cases by the clinicians based on clinical and epidemiological criteria and consequently treated.

Conclusions: In our experience, in a context of high pre-test probability, CT scan shows good sensitivity and a consistently higher specificity for the diagnosis of COVID-19 pneumonia than what reported by previous studies, especially when clinical and epidemiological features are taken into account.

Keywords: COVID-19; Diagnostic X-ray radiology; Sars-CoV-2; Tomography; X-ray computed.

Fig. 1

Flowchart of the study. Abbreviation: RT-PCR, reversal transcription polymerase chain reaction.

Fig. 2

Chest CT images of the various pattern of COVID-19 pneumonia in true positive (TP) patients. A) A 36-year-old man with bilateral, peripheral patchy areas of ground-glass opacity (GGO) (axial view). B) A 42-year-old man with bilateral diffuse areas of GGO (axial view). C) A 45-year-old woman with bilateral diffuse areas of consolidation associated with GGO (axial view).

Fig. 3

Chest CT features consistent with COVID-19 pneumonia in TP patients. A) A 60-year-old woman with bilateral patchy areas of GGO (coronal view). B) A 43-year-old woman with bilateral diffuse areas of consolidation associated with GGO (coronal view). C) A 63-year-old man with bilateral diffuse areas of crazy paving (axial view). D) A 39-year-old man with reversed halo sign in the left inferior lobe (axial view).

Fig. 4

Chest CT features non consistent with COVID-19 pneumonia in true negative (TN) patients. Column A) A 32-year-old man with no parenchymal or mediastinal alteration (axial and coronal view). Column B) A 55-year-old woman with “tree-in-bud” alterations in the right upper lobe (axial and coronal view). Column C) A 85-year-old woman with bilateral pleural effusion and CT features consistent with congestive heart failure (CHF) (axial and coronal view).

Fig. 5

Chest CT images of false positive (FP) patients. Column A) A 79-year-old woman hospitalized but not treated for COVID-19; an alternative diagnosis of bacterial pneumonia by E. Coli was formulated. Chest CT shows diffuse areas of consolidation associated with GGO with a prevalent perihilar distribution (axial and coronal view). Column B) A 57-year-old man hospitalized and treated for COVID-19. Chest CT shows bilateral, peripheral patchy areas of GGO with initial consolidation (axial and coronal view).

Fig. 6

Chest CT images of FN patients with confounding features. Column A) A 29-year-old man with no parenchymal or mediastinal alteration (axial and coronal view). Column B) A 86-year-old with diffuse emphysema (axial and coronal view). Column C) A 75-year-old woman with bilateral pleural effusion, multiple areas of consolidation and CT features consistent with CHF (axial and coronal view).