Approach to laboratory tests for inhibitor diagnosis. *Studies of VWF multimers may be useful to demonstrate a decrease in heavy-molecular-weight multimers or differentiate between AVWS and von Willebrand disease. PFA-100, occlusion time; VWF:Ag, VWF antigen assay; VWF:CBA, collagen-binding assay; VWF:Rco, ristocetin cofactor assay.