A-154 Cost-effectiveness of On-site Vs Send-out Measurement of ADAMTS13 Activity in the Management of Acquired Thrombotic Thrombocytopenic Purpura
Authors: Toulon P , Sudria A , Harzallah I 
Published: September 2023

Abstract

Background
Thrombotic thrombocytopenic purpura (TTP) is a rare thrombotic microangiopathy (TMA) caused by congenital or acquired severe deficiency of disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS-13), an enzyme cleaving von Willebrand factor (VWF). ADAMTS-13 deficiency leads to the accumulation of ultra-large VWF multimers, and subsequent platelet aggregation and microthrombi formation. Aside clinical symptoms, the diagnosis of TTP is based thrombocytopenia, hemolytic anemia with the presence of schistocytes, and severely reduced activity of ADAMTS-13 (&lt;10%). As TTP is a life-threatening condition, it is of great importance to shorten the time to the treatment, and according to the French recommendations, the triplet therapy including plasma exchange (PEX), rituximab, caplacizumab, plus corticosteroids, must be administered to patients with suspected TTP until the results of ADAMTS-13 was obtained, and be pursued only in the case of deficiency. Therefore, a rapid ADAMTS-13 testing is critical for early diagnosis and optimal management of acute TTP.

Methods
We compared the cost-effectiveness of a strategy based on on-site measurement of ADAMTS-13 activity using a rapid fully automated chemiluminescent assay (HemosIL AcuStar ADAMTS-13) vs its centralized measurement in a reference laboratory, as it is currently the case at our institution. For that purpose, we created two scenarios based on either its local measurement with a maximum time-to-result of 16 h (assay performed during daytime, 7/7) or its centralized measurement with a median time-to-result of 4 days (range: 2–8, as demonstrated from the 2018–2021 estimates). The triplet therapy was hypothesized to be started on admission and stopped if ADAMTS-13 activity was &gt;10%. In case of ADAMTS-13 activity &lt;10%, an inhibitor screening would be performed at the reference laboratory, as this assay was not expected to be locally implemented. For the calculation, we considered the costs of reagent, shipping/handling of samples to the reference laboratory, laboratory staff workload, reimbursement rates, and treatments administered in patients with suspected TTP until availability of the ADAMTS-13 result.

Results
Based on 2018 to 2021 estimates, there was a mean of 60 prescriptions of ADAMTS-13 activity per year. Most were for the follow-up of TTP patients and for patients with non-TTP TMA. Only seven were for the diagnosis of acute TTP, as suggested by the French score, which was confirmed in four cases (mean values). The local measurement of ADAMTS-13 activity was found to be cost-effective with a 16%-reduction of the costs compared to its centralized measurement in those seven patients with suspected TTP during the first 4 days.

Conclusion
Together with its short turnaround time (33 min) and its full automation, our results suggest that the HemosIL AcuStar ADAMTS-13 activity assay could be an assay of choice to rapidly measure ADAMTS-13 activity in the plasma and thus to establish the diagnosis of acute TTP in emergency settings. Considering the local costs, using the strategy based on the local evaluation of ADAMTS-13 activity led to a 16%-reduction of the overall costs during the first 4 days after admission of the seven patients with suspected acute TTP.