Diagnosing congenital TTP and distinguishing it from iTTP. While some clinical features, such as presentation early in life or a family history of TTP, may support a diagnosis of cTTP, it is virtually indistinguishable from iTTP during an acute episode. The presence of an inhibitor or antibody against ADAMTS13 confirms iTTP. Patients who do not recover ADAMTS13 activity levels over over 10% during clinical remission should undergo ADAMTS13 gene sequencing.