Abnormality of von Willebrand factor Impaired von Willebrand factor collagen binding activity UMLS:C4022618 Reduced ability of von Willebrand factor (vWF) to bind collagen. Abnormal response to collagen as manifested by reduced or lacking ability of plasma von WIllebrand Factor to bind collagen. An ELISA-based assay is typically used; the test is sensitive to loss of von Willebrand Factor high molecular weight multimers. This abnormality may be seen in von Willebrand disease type 1, type 2A, type 2B, and type 3.