Employment of the ADAMTS13 Assay Improved the Accuracy and Efficiency of the Diagnosis and Treatment of Suspected Acquired Thrombotic Thrombocytopenic Purpura
Brad D Barrows, Jun Teruya. Baylor College of Medicine, Houston, TX
Background: Acquired thrombotic thrombocytopenic purpura (A-TTP) is a significant cause of microthrombotic hemolytic anemia requiring rapid diagnosis and treatment in pediatric patients. A-TTP is generally due to a circulating inhibitor of ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13). ADAMTS13 is responsible for the degradation of unusually large von Willebrand factor (ULVWF) multimers. Without ADAMTS13, the ULVWF multimers can indiscriminately attach to platelets precipitating microthrombosis. The primary treatment for A-TTP is therapeutic plasma exchange (TPE), which removes both the ULVWF multimers and ADAMTS13 inhibitor while replenishing ADAMTS13 via plasma infusion. TPE is an expensive and invasive procedure necessitating thoughtful reservation concerning its use as an emergent treatment modality. The ADAMTS13 activity assay has become a reliable screening method in suspected cases of A-TTP. Many hospital labs do not perform the ADAMTS13 assay, requiring sample analysis at an outside lab, delaying diagnostic confirmation by days. Therefore, most cases highly suspicious for A-TTP must be started on TPE before diagnostic confirmation.
Design: In order to determine the diagnostic value of the ADAMTS 13 assay in detecting true cases of A-TTP and directing the efficient use of TPE, a retrospective analysis was performed including ADAMTS 13 activity results collected at our Children's Hospital during 2007–2011. These data were correlated with the use of TPE as a treatment for cases highly suspicious for A-TTP and evaluated for unnecessary patient morbidity and financial cost. TPE cost was calculated to be $4,000 per procedure using fresh frozen plasma as replacement fluid three times (∼$2,000) plus patient preparation and machine operating costs (∼$2000).
Results: Since implementation of the ADAMTS13 assay, 95% of suspected A-TTP cases were ruled out. This prevented unnecessary patient morbidity in addition to the financial burden of TPE.
|ADAMTS 13 Activity||Number of patients||TTP confirmed||TTP ruled out||TPE prevented||Potential treatment costs avoided|