Activation of the contact-phase system in plasma of patients critically ill with COVID-19. (A,C) Western blot analysis (left) of FXII (A) and HK (C) in plasma from patients with moderate or severe COVID-19 (SARS-CoV-2) and donors (healthy subjects). Four of 15 patients with moderate or severe COVID-19 and 3 of 15 donors are represented. Albumin was used as the loading control. The specificity of the antibodies used is shown (right). (B,D) Densitometric analysis of panels A and C, respectively. COVID-19 moderate/severe, n = 15; donor n = 15. (E) PKa-like activity in plasma of patients with moderate (n = 14) or severe (n = 14) COVID-19 and donors (n = 15). (F) Correlation between the levels of intact HK and PKa-like activity in plasma of patients with severe COVID-19 (n = 14). Correlation was performed according to Spearman’s rank correlation coefficient. *P < .05; **P < .01; ***P < .001.