VWF and thrombotic thrombocytopenic purpura: Since one of the clinical manifestations of TTP is kidney injury, which results from systemic TMA induced by severe deficiency of ADAMTS13 with high VWF antigen/ADAMTS13 ratio [30], the correlation between VWF/ADAMTS13 ratio and plasma NGAL may cast light on the elucidation of pathogenesis of AKI after AAA surgery.