ANTIBODY AND ANTIGEN ON TTP OUTCOMES 1 Title : Presenting ADAMTS 13 antibody and antigen levels predict prognosis in immune-mediated Thrombotic Thrombocytopenic Purpura Running Title : ADAMTS 13 antibody and antigen on TTP outcomes

Immune-mediated Thrombotic Thrombocytopenic Purpura (TTP) is a life-threatening disorder caused by antibodies against ADAMTS13. From the United Kingdom TTP registry we undertook a prospective study investigating the impact of the presenting anti-ADAMTS13 IgG antibody and ADAMTS13 antigen on mortality. 312 episodes involving 292 patients over 87 months were included. 68% were female, median age 46 (range 11-88 years) and median presenting ADAMTS13 of <5% (range <5% – 18%). The mortality rate was 10.3% (n=32). 68% of patients had a raised troponin at presentation conferring a six-fold increase in mortality compared to those with normal troponin levels (12.1% vs. 2.0%, p=0.04). 24% had a reduced Glasgow Coma Score (GCS) at presentation with a nine-fold increase in mortality (20% vs. 2.2% for normal GCS at presentation, p<0.0001). Mortality increased with higher anti-ADAMTS13 antibody levels and lower ADAMTS13 antigen levels. Those with antibody levels in the upper quartile (antibody >77%) had a mortality of 16.9% compared to 5.0% for the lowest quartile (antibody <20%) (p=0.004). Those with an antigen level in the lowest quartile (antigen <1.5%) had a mortality of 18% compared to 3.8% for the highest quartile (antigen >11%) (p=0.005). The synergistic effect of anti ADAMTS13 IgG antibody in the upper quartile and ADAMTS13 antigen in the lowest quartile had the highest mortality of 27.3%. We conclude that both anti-ADAMTS13 IgG antibody and ADAMTS13 antigen levels correlate with outcome in TTP with increased cardiac and neurological involvement and increased mortality. For personal use only. on June 4, 2017. by guest www.bloodjournal.org From