Determining extent of COVID-19 pneumonia on CT based on biological variables

Introduction Covid-19 pneumonia CT extent correlates well with outcome including mortality. However, CT is not widely available in many countries. This study aimed to explore the relationship between Covid-19 pneumonia CT extent and blood tests variations. The objective was to determine for the biological variables correlating with disease severity the cut-off values showing the best performance to predict the parenchymal extent of the pneumonia. Methods Bivariate correlations were calculated between biological variables and grade of disease extent on CT. Receiving Operating Characteristic curve analysis determined the best cutoffs for the strongest correlated biological variables. The performance of these variables to predict mild (50% of parenchyma involved) was evaluated. Results Correlations between biological variables and disease extent was evaluated in 168 patients included in this study. LDH, lymphocyte count and CRP showed the strongest correlations (with 0.67, −0.41 and 0.52 correlation coefficient, respectively). Patients were split into a training and a validation cohort according to their centers. If one variable was above/below the following cut-offs, LDH>380, CRP>80 or lymphocyte count
Highlights • Patients with mild respiratory symptoms are not necessarily referred for CT when they are diagnosed with SARS-CoV2 infection. • Previous studies demonstrated than extent of Covid-19 pneumonia on CT is related to patients' outcome. • LDH combined with CRP and lymphocyte count, help predicting parenchymal extent of the pneumonia when CT-scan is not available.