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Context.--Acquired thrombotic thrombocytopenic purpura (A-TTP) is a rare but significant disease requiring rapid diagnosis and treatment. The diagnosis is often difficult because of variability in the presence of specific clinical criteria. The primary etiology of A-TTP involves inhibitors directed against ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13). Literature has shown that the ADAMTS13 activity assay is sensitive and specific for identifying cases of A-TTP, and application of this test as an on-site screening method has not been fully explored. Objective.--Our objective is to determine if the ADAMTS13 activity assay can be used as a successful, on-site diagnostic modality to rapidly identify cases of ATTP and prevent unnecessary use of prophylactic therapeutic plasma exchange. Design.--A retrospective analysis was performed including 152 patients with clinically suspected A-TTP, screened using the ADAMTS13 activity assay. Results were correlated with potential therapeutic plasma exchange treatment for all cases highly suspicious for A-TTP and evaluated for unnecessary patient morbidity and financial cost. Results.--The ADAMTS13 activity assay had an overall sensitivity and specificity of 100% and 99%, respectively. The positive predictive value was 91% and the negative predictive value was 100%. In 95% of the studies ordered, A-TTP was ruled out, leading to decreased patient morbidity and $1.7 million of potential treatment costs avoided. Conclusion.--Implementation of the fluorescence energy transfer-based ADAMTS13 activity assay as a point-ofcare laboratory study decreased patient morbidity while also directing more efficient employment of therapeutic plasma exchange in cases of suspected A-TTP. (Arch Pathol Lab Med. 2014; 138:546-549; doi: 10.5858/arpa.2013-0170-0A), Thrombotic thrombocytopenic purpura (TTP) is a rare disease that was first described in 1925 by Moschcowitz (1) in his report of a young girl with hemolytic anemia, thrombocytopenia, and coma [...]

A response from the author of the article "Use of the ADAMTS13 activity assay improved the accuracy and efficiency of the diagnosis and treatment of suspected acquired thrombotic thrombocytopenic purpura" by Brad D. Barrows and Jun Teruya in the 2014 issue is presented.