VWF and thrombotic thrombocytopenic purpura: One possible mechanism for increased vWF levels might be decreased activity of the vWF-cleaving protease ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) and ADAMTS13 activity has been shown to be reduced in other conditions associated with thrombocytopenia and raised vWF levels, such as bacterial sepsis and thrombotic thrombocytopenic purpura [42].