Abstract Number: PB0304
Meeting: ISTH 2022 Congress
Background: Severe ADAMTS13 deficiency < 10IU/dL is considered diagnostic for TTP. 2020 ISTH guidelines recommend that where the clinical suspicion for TTP is high, treatment should be initiated urgently whilst ADAMTS13 testing is undertaken. Access to ADAMTS13 testing is variable and quantification of ADAMTS13 activity can vary based on the method used. Traditional assays take a few hours to perform. A rapid ADAMTS13 assay is now available, validated in patients with confirmed TTP. For patients where there is a low probability of TTP, the rapid ADAMTS13 assay in early diagnosis requires further evaluation.
Aims: To evaluate the role of the rapid ADAMTS13 assay in acutely unwell patients where the clinical suspicion of TTP is low.
Methods: This was a real time, multicentre study of ADAMTS13 activity testing using the rapid methodology (Acustar, Werfen, Bedford, USA) and ELISA (Technozym, Technoclone, Austria) in parallel in patients referred to regional centres with suspected TTP. Routine clinical and laboratory parameters were collected for each patient at presentation.
Results: Nine UK regional reference laboratories participated in data collection during 2020 and 2021. Twenty patients referred with suspected TTP but felt to have a low clinical probability of TTP were noted to have unexpectedly low ADAMTS13 activity ( < 20 IU/dL). Secondary testing using the ELISA revealed normal range ADAMTS13 activity levels.. Von Willebrand Factor (vWF) and D-Dimer concentrations were found to be significantly raised, beyond published assay limitations.
Conclusion(s): For patients with a low clinical probability of TTP, discrepant results are low prevalence and appear to occur in acutely unwell patients with disease processes including cancer, sepsis and DIC. Raised vWF and D-Dimer levels suggest the presence of an unmeasured confounding measurand that reduces ADAMTS13 activity in rapid assays. Pending further study of the rapid ADMATS13 assay, a suggested approach for clinical and laboratory teams is provided to guide decision-making.
To cite this abstract in AMA style:MacDonald S, Murphy P, Fretwell R, Downey C, Baker P, Foxton E, Lawrence C, Ali A, Jenkins V, Vilar E, Besser M, Symington E, Robinson M, Desborough M, Thomas W, Yong J, Dutt T. Low ADAMTS13 activity rapid assay results in patients with low clinical probability of Thrombotic Thrombocytopaenic Purpura (TTP) – the United Kingdom experience [abstract]. https://abstracts.isth.org/abstract/low-adamts13-activity-rapid-assay-results-in-patients-with-low-clinical-probability-of-thrombotic-thrombocytopaenic-purpura-ttp-the-united-kingdom-experience/. Accessed February 28, 2024.
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