ICU COVID-19 patient serum-induced effects on PLTs during disease. (A-B) ICU COVID-19 (n = 26) or ICU non-COVID-19 control (n = 5) patient serum-induced changes in Δψ as well as PS externalization in wPLTs were analyzed by FC. (C-D) Sera of 4 ICU COVID-19 patients were collected for up to 14 days during hospitalization and analyzed for their ability to induce changes in Δψ as well as PS externalization in wPLTs via FC. Data are presented as mean ± SEM of the measured fold increase (FI) compared with control. The number of patient sera tested is reported in each graph. Dot lines in (A,B) represent the calculated cutoffs determined by testing sera from healthy donors as mean of FI + 2 × SEM. *P < .05, **P < .01, ***P < .001, and ****P < .0001. ns, not significant; FC, flow cytometry; HC, healthy control; Δψ, inner mitochondrial transmembrane potential; N, number of HCs or patients; PS, phosphatidylserine.