VWF and von Willebrand disease (hereditary or acquired): Thus, VWF:Ag cannot be used in isolation since normal VWF:Ag levels do not always exclude VWD (levels will be normal in some type 2B and 2M VWD patients), and abnormal VWF:Ag levels, although potentially consistent with VWD, do not identify VWD type (type 1 or type 2 VWD)?