Functional assays are commonly used to measure the
antibodies of ADAMTS13 found in patients of
thrombotic thrombocytopenic purpura (
TTP). In this study we used an
enzyme-linked immunoassay to analyze the ADAMTS13-binding
IgG levels in six groups of individuals: normal, random hospitalized patients, acute
TTP,
TTP after receiving plasma
therapy,
TTP in remission, and other types of
thrombotic microangiopathy (TMA). The results showed that ADAMTS13-binding
IgG levels were elevated in 100% of the acute
TTP group, 75% of the
TTP group after receiving plasma
therapy, and 40% of the remission group. Overall, the ADAMTS13-binding
IgG levels correlated with the inhibitory activity levels againstADAMTS13 (r = -0.69, P < 0.0001). The assay also detected elevated
IgG binding levels in 5% - 15% of the normal, random, and other TMA control groups. Addition of purified
ADAMTS13 protein to the plasma samples suppressed the
IgG binding in each of the acute
TTP patients, but in none of the non-
TTP groups. Serial measurement in a patient that had two exacerbations of
TTP within the first three weeks revealed that the ADAMTS13 activity levels remained <0.1 U/ml during this period, and the ADAMTS13-binding
IgG remained elevated, suggesting that ADAMTS13 analysis may provide valuable insight to the disease status during the course of
therapy. Analysis of ADAMTS13-binding
IgG is helpful for the diagnosis and management of
TTP.