A previous study showed that in patients with acute acquired thrombotic microangiopathies associated with severe ADAMTS13 deficiency, autoantibodies are detected more frequently by ELISA than by inhibitor assay.3Moreover, the Bethesda assay can detect just anti-ADAMTS13 antibodies that functionally inhibit ADAMTS13, which represents only a part of the complex pathophysiology of the TTP. The gene discussed is ADAMTS13; the disease is thrombotic thrombocytopenic purpura.