IL-6 and CD8+ T cell counts combined are an early predictor of in-hospital mortality of patients with COVID-19

BACKGROUND. Fatal cases of COVID-19 are increasing globally. We retrospectively investigated the potential of immunologic parameters as early predictors of COVID-19. METHODS. A total of 1018 patients with confirmed COVID-19 were enrolled in our 2-center retrospective study. Clinical feature, laboratory test, immunological test, radiological findings, and outcomes data were collected. Univariate and multivariable logistic regression analyses were performed to evaluate factors associated with in-hospital mortality. Receiver operator characteristic (ROC) curves and survival curves were plotted to evaluate their clinical utility. RESULTS. The counts of all T lymphocyte subsets were markedly lower in nonsurvivors than in survivors, especially CD8(+) T cells. Among all tested cytokines, IL-6 was elevated most significantly, with an upward trend of more than 10-fold. Using multivariate logistic regression analysis, IL-6 levels of more than 20 pg/mL and CD8(+) T cell counts of less than 165 cells/mu L were found to be associated with in-hospital mortality after adjusting for confounding factors. Groups with IL-6 levels of more than 20 pg/mL and CD8(+) T cell counts of less than 165 cells/mu L had a higher percentage of older and male patients as well as a higher proportion of patients with comorbidities, ventilation, intensive care unit admission, shock, and death. Furthermore, the receiver operating curve of the model combining IL-6 (>20 pg/mL) and CD8(+) T cell counts (<165 cells/mu L) displayed a more favorable discrimination than that of the CURB-65 score. The Hosmer-Lemeshow test showed a good fit of the model, with no statistical significance. CONCLUSION. IL-6 (>20 pg/mL) and CD8(+) T cell counts (<165 cells/mu L) are 2 reliable prognostic indicators that accurately stratify patients into risk categories and predict COVID-19 mortality.