Study design and patient selection
In this retrospective cohort study, all adult patients (age ≥18 years old)who were hospitalized due to severe to critical COVID-19, from March 2020 to July 2020, in the Imam Hossein medical center affiliated to Shahid Beheshti University of Medical Sciences, Tehran, Iran, were evaluated15. Patients without positive reverse transcriptase-polymerase chain reaction (rt-PCR) results were excluded and data from patients with a diagnosis of COVID-19 based on rt-PCR were included. The study was conducted based on the declaration of Helsinki and the institutional review board committee approved the study.