Since elevated circulating levels of KL-6 are thought to indicate disruption of the alveolar epithelial lining, we assumed it could be advantageous to analyzing KL-6 in a very severe group of COVID-19 positive patients, with a PaO2/FiO2 ratio ≤100, admitted in ICU for ARDS, who underwent mechanical ventilation. Here, MUC1 is linked to COVID-19.