ADAMTS13 and thrombotic thrombocytopenic purpura: A severe deficiency of ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity < 10 IU/dL is diagnostic of thrombotic thrombocytopenia purpura (TTP) [1,2] and occurs as a result of a congenital deficiency or antibody-mediated autoimmune destruction of ADAMTS13 [1].