title: Frequency and significance of schistocytes in TTP/HUS patients at the discontinuation of plasma exchange therapy.
abstract: BACKGROUND
  Thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS) is characterized by thrombocytopenia, a microangiopathic hemolytic anemia (presence of schistocytes) and elevated LDH without another likely explanation. Standard of care is daily plasma exchange, which is typically discontinued when the platelet count exceeds 100-150 x 10(9)/L for 2 days. However, residual schistocytosis, the presence of schistocytes at the time of discontinuation of plasma exchange therapy, is often disconcerting. We evaluated the frequency and significance of residual schistocytosis in TTP/HUS patients when the patients' platelet counts returned to normal levels (e.g., 100-150 x 10(9)/L).
  
  
  METHODS
  Retrospective review in our institution from 01/1999-03/2004 of all patients treated with plasma exchange for TTP/HUS with at least 2 months of follow-up for relapse was completed. Patients were excluded if the clinical course was complicated by HIV, stem cell/bone marrow and solid organ transplant, pregnancy and auto-immune disease. Schistocytes were documented on day of presentation and on the day the platelet count reached 150 x 10(9)/L. Grading scale (using 100 x objective-a high power field, with approximately 100 red blood cells per field) for schistocytes was as follows: rare for 1 schistocyte per every other other field, 1+ for 1-5%, 2+ for 6-15%, and 3+ for >15%. The frequency of schistocytes was compared to frequency of relapse within 2 months, using Fisher's exact test.
  
  
  RESULTS
  We identified 57 patients with TTP/HUS who received plasma exchange therapy. Of these patients, 12 did not have a follow-up microscopic examination of a peripheral blood smear at discontinuation of plasma exchange therapy and were excluded from further analysis. Of the remaining 45 patients, 16 had residual schistocytosis (35.6%). There was no statistically significant difference in relapse rate with or without residual schistocytosis (P = 1.00, Fisher's Exact test, 2 sided).
  
  
  CONCLUSIONS
  In this study, we found that the presence of residual schistocytosis is common (35.6%). The presence of residual schistocytosis, however, was not predictive of relapse.
authors.affiliation: Department of Pathology and Laboratory Medicine, University of North Carolina, Chapel Hill, NC, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Egan
authors.forename: Shauna N
authors.initials: SN
authors.lastname: Hay
authors.forename: Mark E
authors.initials: ME
authors.lastname: Brecher
mesh_terms: D004913:Erythrocytes, Abnormal / Q000378:metabolism*; D006463:Hemolytic-Uremic Syndrome / Q000097:blood* / Q000628:therapy*; D006801:Humans; D010951:Plasma Exchange; D010976:Platelet Count; D011697:Purpura, Thrombotic Thrombocytopenic / Q000097:blood* / Q000628:therapy*; D012008:Recurrence; D012189:Retrospective Studies; D013997:Time Factors