The Role of ABO Blood Group In TTP Prevalence and Disease Outcome

Abstract 4671

TTP results from deficiency of ADAMTS13 that leads to accumulation of high molecular weight multimers (HMWM) of von Willebrand factor (VWF) and thrombosis in the microvasculature. Previous studies have shown that HMWM VWF purified from blood group O individuals were cleaved faster by ADAMTS13 compared to HMWM VWF from non-O blood group individuals. We hypothesized that blood group O patients have lower prevalence of TTP and/or less severe form of TTP. We conducted a retrospective chart review of all TTP patients treated at our institution from 1993 to 2010. The patients were identified from the review of plasmapheresis treatment records. Any patients with missing charts were excluded. The diagnosis of TTP was made on the basis of laboratory evidence of microangiopathic hemolytic anemia and thrombocytopenia and neurologic and/or renal abnormalities, following exclusion of alternative diagnoses. ADAMTS13 levels were determined by collagen binding assay in select patients. 94 patients were included in the study. The patient characteristics were as follows: 32 males versus 62 females, mean age 45.4 years. 37/94 (39%) patients had ADAMTS13 analyzed with the following results: low ADAMTS13 (21 patients), normal ADAMTS13 (15 patients), equivocal 1. Presentation laboratory investigations were available for 91 patients and were as follows: median platelet count 16×10⁹/L (min 3, max 274) and median hemoglobin 89 g/L (min 48, max 152). At presentation, 19/91 (20.9%) patients had fever (>38C) and 43/91 (47%) had neurological abnormalities (ranging in severity from headache to seizures and decreased level of consciousness). The blood group distribution in the TTP cohort was blood group O 41 patients, non-O 48 patients, data not available 5 patients. All patients received plasmapheresis with cryosupernatant plasma (CSP) or FFP, with some also receiving steroids and other therapies. The patients received a median of 12 (min 1, max 67) plasmapheresis treatments. Overall mortality rate was 22%. The other outcomes were as follows: death at 6 months follow-up 19%; death at 6 months or relapse 20%, death during treatment or permanent dialysis or permanent neurological disability 21%. The prevalence of blood group O versus non-O in our TTP cohort (n=89) was not significantly different from the prevalence of blood group O versus non-O in the general patient population of our institution over 2000–2010 (n=24,852; p=0.71). As illustrated below, in univariate analysis, TTP patients with blood group O did not have significantly different outcomes compared to TTP patients with non-O group blood.