Screening assay detects VWF-specific antibodies among type 3 VWD cohort. Patients enrolled in the Zimmerman Program were screened for IgG (●) and IgM (■) antibodies that bind to rVWF by ELISA. High-titer positive control (+ Ctrl) and negative control (T3 Ab^–) plasma was run on every test plate. Fifty-one healthy controls (HCs) established a threshold for positivity (dotted lines). This initial screen detected 15 of 49 patients with type 3 VWD (Type 3) positive for either IgG (11/49) or IgM (4/49) anti-VWF antibodies.