Development and Performance of the GTI Diagnostics ADAMTS-13 Activity Assay (ATS-13™) and ADAMTS-13 Inhibitor Assay (ATS-13™ INH).

Thrombotic Thrombocytopenic Purpura (TTP) is a disease characterized by the sudden onset of a classical pentad of symptoms: thrombocytopenia, fever, renal insufficiency, neurologic deficit, and microangiopathic hemolytic anemia. ADAMTS-13 is the protease responsible for cleaving von Willebrand Factor (VWF); decreased levels or deficiency of ADAMTS-13 activity has been demonstrated in the plasma of TTP patients. The lack of ADAMTS-13 activity results in the accumulation of multimers of VWF in the plasma and ultimately intravascular platelet aggregation resulting in the clinical symptoms associated with TTP. The presence or absence of inhibitory antibodies directed against ADAMTS-13 influences the treatment protocol for these patients. GTI has developed a rapid, quantitative assay for ADAMTS-13 activity that is based on the cleavage of a von Willebrand Factor substrate and subsequent fluorescent detection. A method comparison was done of GTI’s ADAMTS-13 Activity Assay (n=397) using normal plasma, plasma from suspected TTP patients, and plasma from patients suspected to have other coagulation diseases (ITP, HUS, HIT, APS). All samples were also run on the collagen-binding (n=197) or the Furlan method (n=200) for comparison. This data demonstrated good correlation. Assay precision (with-in run, n=20 and assay-to-assay, n=40) was evaluated and there was less than 20% cv total imprecision for samples with levels of activity across the assay range. In addition, GTI has developed an assay for the semi-quantitative detection of inhibitory antibodies directed against the ADAMTS-13 protease. This assay is similar in format and principle to our ATS-13™ kit; however inhibition of the ADAMTS-13 protease activity is determined in the patient’s heat-inactivated sample following mixing with a provided control at a single dilution. Assay precision and preliminary method comparison data will be presented.