LAUSR

that her persistent thrombocytopenia was caused by sepsis, not refractory TTP. In Patient 10, TTP was unresponsive to multiple treatments, in addition to PEX, corticosteroids, and rituximab. Plus, ADAMTS13 activity was not measured during her course, but we assume that her inhibitory anti-ADAMTS13 antibody titer remained high, and her ADAMTS13 activity remained undetectable. We believe that caplacizumab could have maintained a normal platelet count until prolonged immunosuppression, such as with maintenance rituximab, could establish a remission. The frequency of unpreventable deaths among the 90 patients enrolled in the Oklahoma Registry, from 1995 to 2018, was 7%. During the past 10 years, from 2009 to 2018, there has been only one death (3%) among 31 patients (Figure S1), which we believe was not preventable (patient 11). This suggests that current management and more prompt recognition of TTP have prevented deaths. Even with current management, caplacizumab may prevent additional deaths by providing prompt, durable platelet count responses. Beyond these advances, urgent care protocols for patients with suspected TTP will be required to achieve the maximum possible survival.