The response of a patient with thrombotic thrombocytopenic purpura (TTP) to therapy can be classified using the criteria of Zahn et al. The authors are from the Johns Hopkins University in Baltimore.



complete response

platelet recovery during plasma exchange therapy or within 1 week of stopping treatment


recurrent thrombocytopenia after a response, requiring resumption of daily plasma exchange 1 to 29 days without a plasma exchange


complete response with no need for plasma exchange for >= 30 days


recurrence of TTP after a remission


Platelet recovery was defined as a platelet count >= 150,000 per µL (lower limit of the normal reference range) for >= 3 consecutive days.


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