Diagnosis of thrombotic thrombocytopenic purpura: easy-to-use fiber optic surface plasmon resonance immunoassays for automated ADAMTS-13 antigen and conformation evaluation

Background Laboratory diagnosis of immune-mediated thrombotic thrombocytopenic purpura (iTTP) remains challenging when ADAMTS13 activity ranges between 10-20%. To prevent misdiagnosis, open ADAMTS13 conformation gained clinical attention as a novel biomarker especially to diagnose acute iTTP in patient with diagnostic undecisive ADAMTS13 activity. Plasma ADAMTS13 conformation analysis corrects for ADAMTS13 antigen with both parameters being characterized in enzyme-linked immunosorbent assay (ELISA)-based reference assays requiring expert technicians. Objectives To design ADAMTS13 antigen and conformation assays on automated, easy-to-use fiber-optic surface plasmon resonance (FO-SPR) technology to promote assay accessibility and diagnose challenging iTTP patients. Patients/Methods ADAMTS13 antigen and conformation assays were designed on FO-SPR technology. Plasma of twenty healthy donors and twenty acute iTTP patients were quantified and data from FO-SPR and ELISA reference assays were compared. Results Following assay design, both antigen and conformation FO-SPR assays were optimized and characterized presenting strong analytical sensitivity (detection limit of 0.001 μg/mL) and repeatability (inter-assay variation of 14.4%). Comparative analysis suggests positive correlation (Spearman r of 0.92) and good agreement between FO-SPR and ELISA assays. As expected, FO-SPR assays showed a closed or open ADAMTS13 conformation in healthy donors and acute iTTP patients respectively. Conclusions Both ADAMTS13 antigen and conformation assays were transferred onto automated, easy-to-use FO-SPR technology displaying potent analytical sensitivity and reproducibility. ADAMTS13 antigen and conformation were determined for healthy donors and acute iTTP patients showing strong correlation with ELISA reference. Introducing FO-SPR technology in clinical context could support routine diagnosis of acute iTTP patients, notably when ADAMTS13 activity fluctuates between 10-20%.