GDF15 and COVID-19: Our results are consistent with recent studies that have found that increased circulating levels of GDF15 and ACE2 are associated with a poor prognosis in patients with COVID-19 (Notz et al., 2020; Myhre et al., 2020; Luis García de Guadiana et al., 2021; Lundström et al., 2021; van Lier et al., 2021).