Studied patient cohorts (a) and comparison of their proteome profiles using principal component analysis (PCA) (b). (a) Between November and December 2021, COVID-19 patients (n = 19) admitted to the HDZ NRW in the ICU were included in this study. The highly purified platelets were prepared within two days after patient admission. The majority of patients died (ICU A, n = 11). Two patients had no identifiable outcome, as they were transferred to other hospitals (ICU N). Six patients survived and were transferred to the normal ward (ICU B). The platelets of five of these patients could be prepared at this time point (NW). The control group included age- and sex-equivalent healthy blood donors. (b) PCA, based on 721 PGs quantified with LFQs in all the samples, showed a distinct clustering of ICU patients (ICU A, non-survivors: red; ICU B, survivors: orange; ICU N, unknowns: gray), NW patients (green), and healthy controls (blue).