KRT18 and acute respiratory distress syndrome: To determine the alveolar epithelial cell death patterns in COVID-19 patients with or without ARDS, we analyzed the serum levels of full-length (CK18-M65 antigen) and caspase-cleaved (CK18-M30 antigen) cytokeratin 18, which are epithelial total cell death and epithelial apoptosis markers, respectively, in addition to the other several alveolar epithelial and endothelial injury markers.