Chest computed tomography and alveolar-arterial oxygen gradient as rapid tools to diagnose and triage mildly symptomatic COVID-19 pneumonia patients

de Roos, Marlise P.; Kilsdonk, Iris D.; Hekking, Pieter-Paul W.; Peringa, Jan; Dijkstra, Nynke G.; Kunst, Peter W.A.; Bresser, Paul; Reesink, Herre J.

PURPOSE: In pandemic COVID-19, a rapid clinical triage is crucial to determine which patients are in need for hospitalisation. We hypothesised that chest CT and alveolar-arterial oxygen (A-a) gradient may be useful to triage these patients, since it reflects the severity of the pneumonia-associated ventilation/perfusion abnormalities. METHODS: A retrospective analysis was performed in consecutive patients (n=235) suspected for COVID-19. The diagnostic protocol included low-dose chest CT and arterial blood gas analysis. In patients with CT-based COVID-19 pneumonia, the association between “need for hospitalisation” and A-a gradient was investigated by multivariable logistic regression model; and, the A-a gradient was tested as predictor for need for hospitalisation using ROC curve analysis and logistic regression model. RESULTS: 72 out of 235 patients (mean±sd age 55.5±14.6 years, 40% female) screened by chest CT showed evidence for COVID-19 pneumonia. In these patients, A-a gradient was shown to be a predictor of need for hospitalisation, with an optimal decision level (“cut-off”) of 36.4 mmHg (95% CI 0.70–0.91, p<0.001). The A-a gradient was shown to be independently associated with need for hospitalisation (OR 1.97 [95% CI 1.23–3.15], p=0.005, A-a gradient per 10 points) from CT-SS (OR 1.13 [95% CI 0.94–1.36], p=0.191), NEWS (OR 1.19 [95% CI 0.91–1.57], p=0.321) or peripheral oxygen saturation (OR 0.88 [95% CI 0.68–1.14], p=0.345). CONCLUSION: Low dose chest CT and the alveolar-arterial oxygen gradient may serve as rapid and accurate tools to diagnose COVID-19 pneumonia and to select mildly symptomatic patients in need for hospitalisation.