TNF and COVID-19: As we mentioned above, extracorporeal blood purification treatment can effectively remove IL-6, IL-8, IL-1β, TNF-α and so on [13], however, due to the expenditures associated with measuring various inflammatory cytokines as well as the unavailability of some laboratory kits in initial and peak periods of COVID-19 epidemic in Iran, and considering the interleukin 6 as one of the most important inflammatory cytokines, only this cytokine has been measured in this research.