SFTPD and acute respiratory distress syndrome: Our main results are summarized as follows: (1) higher baseline levels of SP-D in serum on the day of hospital admission is an independent but weak risk factor for developing ARDS; (2) on the other hand, the kinetics of circulating SP-D during SARS-CoV-2 infection is an independent protective element from developing ARDS, reducing the risk of ARDS by a factor of 50 when it increases from D1 to D5 of analysis (7–12 days after first symptoms).