Unaltered in vitro bleeding time in sepsis or COVID-19. (A-D) In vitro bleeding time was mimicked using PFA-200 in whole blood (minimal platelet count > 150/nL). Representative figures are displayed in panels C and D. Arrows indicate sawtooth pattern–like events. Reference ranges are highlighted in panels A and B. (E-N) Thrombus and fibrin formation were assessed under venous shear (200 s−1) using recalcified whole blood on collagen/tissue factor (TF) (E-J) or collagen-coated spots (K-N). Samples were stained for platelets (α-GPIbβ-Alexa647, magenta) and fibrin(ogen) (cyan). Panels F and K show surface area coverage (SAC, %) of platelets, panels G and L show platelet fluorescence intensity in arbitrary units (AUs), panels H and M show the morphological score evaluated by 2 blinded investigators, and in panels I and N, fibrin(ogen) SAC are displayed. Representative images from 1 focal plane are depicted in panel E. Scale bars indicate 50 μm. In panel J, thrombi were imaged in 1 focal plane using confocal microscopy. Scale bar in upper images indicates 50 μm and lower images indicates 25 μm. All graphs show median ± 95% CI. Differences were analyzed using the Kruskal-Wallis test. Col/ADP, collagen/ADP; Col/Epi, collagen/epinephrine; hep, heparin.
