Accuracy of CT in a cohort of symptomatic patients with suspected COVID-19 pneumonia during the outbreak peak in Italy

Abstract

Objective: To assess sensitivity/specificity of CT vs RT-PCR for the diagnosis of COVID-19 pneumonia in a prospective Italian cohort of symptomatic patients during the outbreak peak.

Methods: In this cross-sectional study, we included all consecutive patients who presented to the ER between March 13 and 23 for suspected COVID-19 and underwent CT and RT-PCR within 3 days. Using a structured report, radiologists prospectively classified CTs in highly suggestive, suggestive, and non-suggestive of COVID-19 pneumonia. Ground-glass, consolidation, and visual extension of parenchymal changes were collected. Three different RT-PCR-based reference standard definitions were used. Oxygen saturation level, CRP, LDH, and blood cell counts were collected and compared between CT/RT-PCR classes.

Results: The study included 696 patients (41.4% women; age 59 ± 15.8 years): 423/454 (93%) patients with highly suggestive CT, 97/127 (76%) with suggestive CT, and 31/115 (27%) with non-suggestive CT had positive RT-PCR. CT sensitivity ranged from 73 to 77% and from 90 to 94% for high and low positivity threshold, respectively. Specificity ranged from 79 to 84% for high positivity threshold and was about 58% for low positivity threshold. PPV remained ≥ 90% in all cases. Ground-glass was more frequent in patients with positive RT-PCR in all CT classes. Blood tests were significantly associated with RT-PCR and CT classes. Leukocytes, lymphocytes, neutrophils, and platelets decreased, CRP and LDH increased from non-suggestive to suggestive CT classes.

Conclusions: During the outbreak peak (in a high-prevalence setting), CT presented high PPV and may be considered a good reference to recognize COVID-19 patients while waiting for RT-PCR confirmation.

Key points: • During the epidemic peak, CT showed high positive predictive value and sensitivity for COVID-19 pneumonia when compared with RT-PCR. • Blood tests were significantly associated with RT-PCR and CT classes.

Keywords: COVID-19; Pneumonia; Polymerase Chain Reaction; Severe acute respiratory syndrome coronavirus 2; Tomography, X-ray computed.

Fig. 1

Exemplification of classification of CT findings: a CT findings highly suggestive of COVID-19 pneumonia, with bilateral interstitial involvement, patchy ground-glass opacities (arrow), and peripheral consolidations (*), confirmed by positive RT-PCR; b CT findings suggestive of COVID-19 pneumonia, with unilateral peripheral consolidation and subtle ground-glass opacities, confirmed by positive RT-PCR; c CT findings non-suggestive of COVID-19 pneumonia, with mostly unilateral bronchial wall thickening, endobronchial secretions, tree-in-bud nodules, and consolidation, confirmed by negative RT-PCR

Fig. 2

Visual scoring system used to classify the extension of parenchymal involvement: < 20% (a), 20–40% (b), 40–60% (c), and > 60% (d)

Fig. 3

Flowchart representing the study population and the subgroups with different combinations of CT and RT-PCR results

Fig. 4

Examples of discordant cases between CT and RT-PCR. a Focal polygonal consolidation without ground-glass opacity, considered as non-suggestive at CT scan but resulting in positive RT-PCR test. b Bilateral (mostly right) patchy ground-glass opacities, with small areas of consolidation, which was classified as highly suggestive, resulting in a first negative RT-PCR, followed by a positive RT-PCR performed 7 days later