# A comparative study of anti–ADAMTS-13 antibody dynamics in immune-mediated thrombotic thrombocytopenic purpura

## TL;DR

This study compares two lab tests for measuring ADAMTS-13 activity and antibodies in immune-mediated thrombotic thrombocytopenic purpura, finding they agree on activity but differ in antibody detection during remission.

## Contribution

The study reveals significant differences in anti–ADAMTS-13 antibody detection between CLIA and ELISA in patients with partial ADAMTS-13 activity during remission.

## Key findings

- CLIA and ELISA show strong agreement in measuring ADAMTS-13 activity.
- Significant discrepancies in anti–ADAMTS-13 antibody detection occur in remission patients with 10–50% ADAMTS-13 activity.
- CLIA detects antibodies earlier than ELISA in predicting iTTP relapses.

## Abstract

Thrombotic thrombocytopenic purpura, particularly its immune-mediated variant (iTTP), necessitates accurate diagnostic approaches for effective management.

To compare a chemiluminescence immunoassay (CLIA) and an enzyme-linked immunosorbent assay (ELISA) for testing ADAMTS-13 activity and detecting anti–ADAMTS-13 autoantibodies (AAbs) in patients with iTTP.

This study involved 31 paired samples from 12 iTTP patients. ADAMTS-13 activity was measured using the HemosIL AcuStar (Instrumentation Laboratory, CLIA) and Technozym (Technoclone) activity assay (ELISA). The presence of AAbs was assessed using Technozym ADAMTS-13-INH assay (ELISA) and HemosIL AcuStar activity (CLIA) within a Bethesda assay following mixing with normal pool plasma. von Willebrand factor (VWF) multimers were analyzed using the HYDRASYS-2 SCAN system and the HYDRAGEL 5- or 11-VW Multimer kits (Sebia). VWF activity levels were measured with the HemosIL AcuStar VWF:GPIbR on the ACL AcuStar Analyzer (IL).

For ADAMTS-13 activity, a strong linear relationship and no bias between CLIA and ELISA were confirmed (slope = 1.01 [0.91, 1.11], intercept = 0.00 [−0.47, 0]). However, significant discrepancies were found in AAb detection during remission phases with ADAMTS-13 activity between 10% and 50%, with CLIA and ELISA showing significant divergence (P < .001, Cohen’s g = 0.34). Consistently, VWF multimers and activity levels exhibited significantly different values between remission samples with ADAMTS-13 activity below 50% and above 50%. In longitudinal analysis of patients with multiple iTTP relapses, positivity to CLIA appears to precede ELISA in predicting exacerbations.

While CLIA and ELISA might be interchangeable for assessing ADAMTS-13 activity, they are not equivalent for detecting AAbs, particularly in patients in clinical remission with ADAMTS-13 activity between 10% and 50%.

•Immune-mediated thrombotic thrombocytopenic purpura (iTTP) requires accurate diagnostics.•This study compared chemiluminescence-based immunoassay and enzyme-linked immunosorbent assay for ADAMTS-13 activity and anti–ADAMTS-13 antibody in immune-mediated thrombotic thrombocytopenic purpura.•ADAMTS-13 activity measurement was similar by both methods; anti–ADAMTS-13 autoantibody detection differed significantly.•The difference is focused in patients in clinical remission with ADAMTS-13 activity between 10% and 50%.

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) requires accurate diagnostics.

This study compared chemiluminescence-based immunoassay and enzyme-linked immunosorbent assay for ADAMTS-13 activity and anti–ADAMTS-13 antibody in immune-mediated thrombotic thrombocytopenic purpura.

ADAMTS-13 activity measurement was similar by both methods; anti–ADAMTS-13 autoantibody detection differed significantly.

The difference is focused in patients in clinical remission with ADAMTS-13 activity between 10% and 50%.