Abstract: medRxiv preprint doi: https://doi.org/10.1101/2020.09.05.20184655; this version posted October 27, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC-ND 4.0 International license . Running head: Activin/Follistatin-axis in COVID-19 The Activin/Follistatin-axis is severely deregulated in COVID-19 and independently associated with in-hospital mortality Evgenia Synolaki1, Vasileios Papadopoulos2*, Georgios Divolis1*, Olga Tsahouridou3, Efstratios Gavriilidis2, Georgia Loli3, Ariana Gavriil1, Christina Tsigalou4, Nikolaos R. Tziolos5, Eleni Sertaridou6, Bhanu Kalra7, Ajay Kumar7, Petros Rafailidis8, Arja Pasternack9, Dimitrios T. Boumpas5, Georgios Germanidis3, Olli Ritvos9, Simeon Metallidis3, Panagiotis Skendros2,10,# and Paschalis Sideras1,# 1 Biomedical Research Foundation Academy of Athens, Center for Clinical, Experimental Surgery & Translational Research, Athens, Greece; 2First Department of Internal Medicine, University Hospital of Alexandroupolis, Democritus University of Thrace, Alexandroupolis, Greece; 3First Department of Internal Medicine, AHEPA University Hospital, Aristotle University of Thessaloniki, Thessaloniki, Greece; 4 Laboratory of Microbiology, University Hospital of Alexandroupolis, Democritus University of Thrace, Alexandroupolis, Greece; 5Fourth Department of Internal Medicine, Attikon University Hospital, National and Kapodistrian University of Athens Medical School, Athens, Greece; 6Intensive Care Unit, University Hospital of Alexandroupolis, Alexandroupolis, Greece; 7AnshLabs, Webster, Texas, USA; 8Second Department of Internal Medicine, University Hospital of Alexandroupolis, Democritus University of Thrace, Alexandroupolis, Greece; 9 Department of Physiology, Faculty of Medicine, University of Helsinki, Helsinki, Finland; 10Laboratory of Molecular Hematology, Democritus University of Thrace, Alexandroupolis, Greece; 1 NOTE: This preprint reports new research that has not been certified by peer review and should not be used to guide clinical practice. medRxiv preprint doi: https://doi.org/10.1101/2020.09.05.20184655; this version posted October 27, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC-ND 4.0 International license . * These authors contributed equally to the study. # These authors supervised equally the study. Corresponding author: Dr. Paschalis Sideras; Biomedical Research Foundation Academy of Athens, Center for Clinical, Experimental Surgery & Translational Research, Athens, Greece; tel: +302106597183; e-mail: sideras@bioacademy.gr 2 medRxiv preprint doi: https://doi.org/10.1101/2020.09.05.20184655; this version posted October 27, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC-ND 4.0 International license . Potential conflicts of interest: Authors BK and AK are employees of Ansh Labs, which is the manufacturer of the ELISA kits used in this study. The rest of the authors declare no conflict of interest. Funding Support: This work was supported by grants from the General..