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Clinical implications of ADAMTS-13 conformation ELISA in immune-mediated thrombotic thrombocytopenic purpura with
Mikiya Kajita1, Kazuya Sakai2, Quintijn Bonnez3
1Department of Blood Transfusion Medicine, Nara Medical University, Kashihara, Japan; Department of Hematology, Gunma University Graduate School of Medicine, Maebashi, Japan.
Background:
Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a fatal thrombotic disorder caused by anti-ADAMTS-13 autoantibodies. ADAMTS-13 conformation is a promising biomarker for diagnosing and monitoring iTTP; however, its utility in Japanese patients is limited owing to undetectable acute-phase ADAMTS-13 antigen levels.
Objectives:
This study aimed to investigate whether ADAMTS-13 conformational changes can be detected even when ADAMTS-13 antigen levels are undetectable for conventional assays.
Methods:
In this retrospective study, samples were obtained at initial presentation from 25 Japanese patients with acute iTTP and 21 healthy donors. We used purified patient immunoglobulin (Ig)Gs to open up closed ADAMTS-13 in normal plasma (patient IgG-based conformation ELISA). The conformation index cutoff was 0.3 for the patient IgG-based assay. Conventional conformation ELISA was also performed when antigen levels were ≥0.03 μg/mL.
Results:
The patient IgG-based assay demonstrated a closed-to-open conformational shift in all patients, enabling acute-phase assessment irrespective of antigen levels. Only 9 patients met the antigen threshold required for the conventional assay, and all demonstrated an open conformation. Over a median follow-up of 283 days, 5 patients experienced clinical relapse. Four patients showed an open conformation prior to relapse in both assays. When antigen levels were detectable, the patient IgG-based assay showed high concordance with the conventional assay.
Conclusion:
The patient IgG-based assay may help overcome the limitation imposed by low antigen levels during the acute phase in most Japanese patients with iTTP, enabling conformational assessment at presentation. Conformation ELISA may be useful for predicting relapse in Japanese patients with iTTP.
