ADAMTS13 Antigen together to collagen binding to von Willebrand Factor (VWF:CB) and VWF Antigen (VWF:Ag) were potential markers of acute disease severity in acquired thrombotic thrombocytopenic purpura (aTTP)

Abstract

Background : The reduced levels of circulating ADAMTS13 antigen (Ag), at first presentation in patients (P) with non- inhibitory antibodies (ab), appear to be a major determinant of disease severity in aTTP (Thomas, 2015). Lack of larger VWF multimers was strongly correlated with low VWF:CB/VWF:Ag and the ratio could be a marker of crisis severity aTTP (Lotta, 2011).Aims : To evaluate the relationship between ADAMTS13 parameters and other laboratory markers to the severity of aTTP crisis in 57P.Methods : ADAMTS13 activity, Ag, free IgG, IgM, IgA anti-ADAMTS13 ab, VWF:CB collagen type I, VWF:Ag were evaluated (ELISA). Detection of circulating immune complexes (CIC) was done by A) ELISA with mouse monoclonal ab anti- ADAMTS13 (ABCAM) and anti- human IgG- HRP and B) ADAMTS13Ag kit and anti- humanIgG- HRP. Assessment of von Willebrand multimers by normalized multimer ratio. Interquartile Range (IQR) was obtained using normal plasma. Other variables were reported: platelet count, hematocrit, hemoglobin, white blood cells, and blood group. Informed consent and ethical approval were obtained.Results : Some of our results were reported in Table I. In addition, P usually had their first aTTP episode between their 19 and 74 years. Prevalence of women was 82%. CIC median of positive P (n=10) was 0.52 (IQR, 0.51- 0.65)We verified normal distribution of CIC, VWF:CB, VWF:Ag, Hematocrit, VWF:CB/VWF:Ag, and normalized multimers, whereas ADAMTS13 Ag needed to be Ln- transformed. Correlations were showed in Table II.A multiple linear regression model was applied to generate a more precise estimate of parameters. The result was Ln (ADAMTS13Ag)=- 2.343+0.017VWF:CB- 0.012VWF:Ag.Conclusions : In our cohort, 25% of P tested positive CIC, therefore during aTTP crisis do not seem to be a biomarker of disease severity.We can predict a value of Ln ADAMTS13 Ag from the values of VWF:CB and VWF:Ag. These variables can be candidate markers of disease severity in aTTP as ADAMTS13 Ag is.