VWF antibody titer analysis. (A) Titration curves of antibody-positive type 3 VWD samples (patient IDs left of curves) confirm and semiquantify VWF antibody presence. Patient plasma was titrated in blocking buffer and screened by ELISA to determine maximum dilution where anti-VWF antibody OD remained above the 95th percentile cut points as determined by the HC cohort. (B) Distribution of antibodies that inhibited VWF binding to factor FVIII, collagens type III and IV, and platelet receptor GPIbα (F8B, CB3, CB4, and GPIbM accordingly) along the x-axis by antibody titer level on the y-axis (abbreviated to titer value without 1: prefix; eg, 1:25 = 25). (C) Correlation of VWF antibody titer from none detected (ND) to 1:6400 on x-axis (abbreviated as in panel B) with A.U. measured by ELISA using calibration curves. Symbols represent plasma samples and are differentiated into IgG (black) and IgM (gray) anti-VWF immunoglobulins (Igs), healthy control (▴), type 3 VWD antibody–positive (•), or positive control (★).