COVID-19 pneumonia: high diagnostic accuracy of chest CT in patients with intermediate clinical probability

Abstract

Objectives: To assess inter-reader agreements and diagnostic accuracy of chest CT to identify COVID-19 pneumonia in patients with intermediate clinical probability during an acute disease outbreak.

Methods: From March 20 to April 8, 319 patients (mean age 62.3 years old) consecutive patients with an intermediate clinical probability of COVID-19 pneumonia underwent a chest CT scan. Two independent chest radiologists blinded to clinical information and RT-PCR results retrospectively reviewed and classified images on a 1-5 confidence level scale for COVID-19 pneumonia. Agreements between radiologists were assessed with kappa statistics. Diagnostic accuracy of chest CT compared with RT-PCR assay and patient outcomes was measured using receiver operating characteristics (ROC). Positive predictive value (PPV) and negative predictive value (NPV) for COVID-19 pneumonia were calculated.

Results: Inter-observer agreement for highly probable (kappa: 0.83 [p < .001]) and highly probable or probable (kappa: 0.82 [p < .001]) diagnosis of COVID-19 pneumonia was very good. RT-PCR tests performed in 307 patients were positive in 174 and negative in 133. The areas under the curve (AUC) were 0.94 and 0.92 respectively. With a disease prevalence of 61.2%, PPV were 95.9% and 94.3%, and NPV 84.4% and 77.1%.

Conclusion: During acute COVID-19 outbreak, chest CT scan may be used for triage of patients with intermediate clinical probability with very good inter-observer agreements and diagnostic accuracy.

Key points: • Concordances between two chest radiologists to diagnose or exclude a COVID-19 pneumonia in 319 consecutive patients with intermediate clinical probability were very good (kappa: 0.82; p < .001). • When compared with RT-PCR results and patient outcomes, the diagnostic accuracy of CT to identify COVID-19 pneumonia was high for both radiologists (AUC: 0.94 and 0.92). • With a disease prevalence of 61.2% in the studied population, the positive predictive values of CT for diagnosing COVID-19 pneumonia were 95.9% and 94.3% with negative predictive values of 84.4% and 77.1%.

Keywords: COVID-19; Disease outbreak; Observer variation; ROC curve; Triage.

Fig. 1

Receiver operating characteristics (ROC) curves for the diagnosis of COVID-19 pneumonia by radiologist 1 (a) and radiologist 2 (b) computed against the results of reverse transcription polymerase chain reaction (disease prevalence: 56.4%)

Fig. 2

Receiver operating characteristics (ROC) curves for the diagnosis of COVID-19 pneumonia by radiologist 1 (a) and radiologist 2 (b) computed against results of reverse transcription polymerase chain reaction after integration of 16 cases of probable diagnosis of COVID-19 pneumonia by both radiologists among COVID-19-positive patients (disease prevalence: 61.6%)

Fig. 3

CT scan of a 51-year-old male patient with positive RT-PCR test for COVID-19 and classified as a highly probable diagnosis by both radiologists. Bilateral and peripheral areas of ground glass opacities in the upper and right middle lobes (a, b) and band-like opacities and consolidations in lung bases (c, d)

Fig. 4

CT scan of a 46-year-old male patient with a negative RT-PCR test but classified as a highly probable diagnosis of COVID-19 pneumonia by both radiologists. Bilateral and peripheral areas of ground glass opacities within the upper lobes (a, b) and in the right lower lobe (c, d)

Fig. 5

CT scan of a 34-year-old female patient with a positive RT-PCR test classified as probable diagnosis of COVID pneumonia by one radiologist and as alternative diagnosis (bronchopneumonia) by the other. Note the presence of two rounded areas of ground glass opacities (yellow arrows) within the right upper lobe (a) and multiple small nodular opacities of ground glass attenuation disseminated in the right lower lobe (a, b, c) and to a lesser extent the left upper lobe (a). Bronchial wall thickening, tree-in-bud sign, and subpleural focal area of consolidation are also visible in the left lower lobe (c)