Predictive Value of Schistocytes in Recurrence of Acquired Thrombotic Thrombocytopenic Purpura With Severe ADAMTS13 Deficiency at Discontinuation of Daily Therapeutic Plasma Exchange.

Acquired thrombotic thrombocytopenic purpura (TTP) is characterized by microangiopathic hemolytic anemia, thrombocytopenia, and commonly ADAMTS13 deficiency. Patients with TTP and severe ADAMTS13 deficiency have high risk of disease recurrence, yet the ability to predict which patients will have recurrence remains limited. We assessed whether the presence of persistent schistocytes in TTP patients with severe ADAMTS13 deficiency at the time of daily therapeutic plasma exchange (TPE) discontinuation was predictive of disease recurrence. We retrospectively reviewed the electronic medical records of all patients with a diagnosis of TTP treated with TPE at our university medical center between August 1991 and April 2013. Exacerbation was defined as disease recurrence within 30 days of cessation of daily TPE, and relapse was defined as disease recurrence >30 days after cessation of daily TPE. Comparisons were performed with a two-sided Fisher's exact test or χ2 test. Of the 46 total TTP patients eligible for analysis, nine had residual schistocytosis (20%), four of the nine (44%) had exacerbations, and two of the nine (22%) relapsed. Of the 37 patients without residual schistocytosis, 16 (43%) had exacerbations and 11 (30%) relapsed. There were no statistically significant differences in the exacerbation or relapse rates with or without residual schistocytosis (P = 1.00 and 1.00, respectively). Residual schistocytes after discontinuation of daily TPE were not uncommon. The persistence of schistocytes had poor sensitivity, specificity, and both positive and negative predictive values. After the initial diagnosis of TTP is made, there is no reason to continue documenting the presence or absence of schistocytes.