Exacerbation-free survival rates in patients with iTTP based on ADAMTS13 activity, ADAMTS13 antigen, and anti-ADAMTS13 IgG. The exacerbation-free survival rates in patients with low (<25th percentile) and high (≥25th percentile) levels of plasma ADAMTS13 activity on admission (A) or in patients with low (<10 IU/dL) and high (≥10 U/dL) levels of plasma ADAMTS13 activity 3 to 7 days after initiation of TPE (B) and at clinical response/remission (C); the exacerbation-free survival rates in patients with low (<25th percentile) and high (≥25th percentile) levels of plasma ADAMTS13 antigen on admission (D), 3 to 7 days after initiation of therapies (E), and at clinical response/remission (F); the exacerbation-free survival rates in patients with high (≥75th percentile or ≥7468.4 U/mL) and low (<75th percentile or < 7468.4 U/mL) levels of plasma anti-ADAMTS13 IgG on admission (G), 3 to 7 days after initiation of therapies (H), and at clinical response/remission (I). P values less than .05 and .01 are considered to be statistically significant and highly significant, respectively.