Association among platelet apoptosis and clinical biomarkers, thromboembolic complications, and mortality. The correlations between platelet apoptosis parameters and PLT count, as well as D-dimer and SOFA score measured at the same day of platelet testing, were assessed. (A-B) An association was observed between PLT count and PS externalization (A) and cytosolic calcium concentration (B). (C) Moreover, a significant correlation was detected for D-dimer and PS externalization. (D) The clinical relevance of PS externalization was assessed using the SOFA score and revealed a significant positive correlation. Pearson’s correlation coefficients were calculated and are shown in the panels. (E-F) The PS externalization (E) and the cytosolic calcium concentration (F) were determined and compared between COVID-19 patients in the ICU depending on the incidence of thromboembolic complications and mortality, respectively. Data are presented as mean of the measured FI compared with control. Not significant, *P < .05, **P < .01, ***P < .001, ****P < .0001. The number of patients and healthy donors tested is reported in each graphic. Dashed lines represent the cutoffs determined from healthy donors as mean of FI + 2× SEM.