ADAMTS13 activity measurements by both immunoblotting and the fluorogenic assay with FRETS-VWF73 substrate. (A) Sixty patients who had ADAMTS13 activity < 10% by at least 1 of the 2 methods of measurement at the time of their initial diagnosis. The solid line represents 33 patients who had ADAMTS13 activity < 5% by both assays, arbitrarily designated as 4%. The broken lines represent each of the 16 patients who had ADAMTS13 activity < 5% by one assay but 5% or more by the other assay. The dotted lines represent each of the 11 patients who had ADAMTS13 activity of 5% to 9% by one assay but more than 10% by the other. (B) The 16 patients who had ADAMTS13 activity < 10% by at least 1 of the 2 methods of measurement at the time of their initial diagnosis and who have relapsed. The solid line represents 10 patients who had ADAMTS13 activity < 5% by both assays, arbitrarily designated as 4%. The broken lines represent each of the 4 patients who had ADAMTS13 activity < 5% by one assay but 5% or more by the other. The dotted lines represent each of the 2 patients who had ADAMTS13 activity of 5% to 9% by one assay but more than 10% by the other.