ADAMTS13 inhibitor and anti-ADAMTS13 IgG autoantibody titers in the Japanese iTTP cohort. ADAMTS13 inhibitor titers (filled circle, n = 195) were determined in a mixing assay using the chromogenic activity ELISA based on the GST-VWF73 fragment and detection of cleaved VWF substrate by the anti-N10 mAb. Total anti-ADAMTS13 IgG autoantibody titers (triangle, n = 195) was determined using ELISA where rADAMTS13 was coated and bound anti-ADAMTS13 autoantibodies were detected. The dotted line indicates cutoff values for ADAMTS13 inhibitor titers and anti-ADAMTS13 IgG autoantibody titers (0.5 BU/mL and 12% TTP-03-A equivalents respectively). mAb, monoclonal antibody.