Significance In this study we have identified a mechanism that links pathophysiological ADAMTS13 deficiency to innate immunity and hemostasis by facilitating monocyte extravasation as a prerequisite for their subsequent on-site differentiation into proinflammatory macrophages under conditions of both physiological laminar flow and disturbed reduced flow, e.g., as occurs at atherosclerosis predilection sites. Our bioassay approach using patients’ plasma may become a useful diagnostic tool to assess ADAMTS13 activity ex vivo under conditions of near-physiological to atherosclerosis-prone arterial blood flow, which seems to be more relevant than the conventional static FRET-based assay method.