 This is multi-centre study within the South East England SEE Thrombotic Thrombocytopenic Purpura TTP study group, primarily involving tertiary centres with expertise in treating TTP, apheresis units and specialist medical professionals. Feedback and discussions with TTP patients during treatment and discussion with those attending out-patient clinics have been incorporated into the development of this study. We have reviewed treatment protocols for TTP patients published in peer reviewed journals and consulted SEE TTP study groups on the study design. Medical professionals with expertise in TTP treatment and management have also been consulted. 