PB1329 - Place of the plasma mixing Bethesda assay to detect anti-ADAMTS13 antibodies for the diagnosis and follow-up of immune thrombotic thrombocytopenic purpura.

Tuesday, June 25, 2024

13:45 – 14:45 ICT

Room: Exhibition Hall

Co-Author(s)

CT

Cheymaa Taleb Ouallal

MD
CHU Lille, Service d'Hemostase et Transfusion
Lille, Nord-Pas-de-Calais, France

Presenting Author(s)

AD

Annabelle Dupont

professor
Univ. Lille, Inserm, CHU Lille, Institut Pasteur de Lille, U1011-EGID, F5900 Lille
59000 Lille, Nord-Pas-de-Calais, France

Co-Author(s)

CZ

Christophe Zawadzki

PharmD
CHU Lille, Service d'Hemostase et Transfusion - Lille FRANCE
Lille, Nord-Pas-de-Calais, France
EJ

Emmanuelle Jeanpierre

PharmD
CHU Lille, Service d'Hemostase et Transfusion - Lille FRANCE
Lille, Nord-Pas-de-Calais, France
AT

Antoine Tournoys

PharmD
CHU Lille, Service d'Hemostase et Transfusion- Lille France
Lille, Nord-Pas-de-Calais, France
MD

Maximilien Desvages

PharmD
CHU Lille, Service d'Hemostase et Transfusion-Lille France
Lille, Nord-Pas-de-Calais, France
SS

Sophie Susen, PhD,MD

Professor of Haematology
Centre Hospitalier Universitaire de Lille, Université de Lille, Lille, France
Lille, Nord-Pas-de-Calais, France
FP

François Provot

MD
CHU Lille, Service de Nephrologie- Lille FRANCE
Lille, Nord-Pas-de-Calais, France
AB

Anne Bauters

PharmD
CHU Lille, Service d'Hemostase et Transfusion - Lille FRANCE
Lille, Nord-Pas-de-Calais, France

Background: Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is a life-threatening disorder caused by immunoglobulin G autoantibodies (IgG-Ab) against ADAMTS13. These IgG-Ab cause acquired deficiency of ADAMTS13, by either increasing clearance or inhibiting function. ITTP diagnosis is based on anti-ADAMTS13-IgG-Ab ELISA detection, independently of Ab effects. Inhibiting function of anti-ADAMTS13-IgG-Ab is detected by plasma mixing Bethesda assay. One japanese study reports for 6 % of patients in a cohort of 195 iTTP, a positive Bethesda test with negative ELISA. This iTTP biological presentation is poorly addressed in the literature.

Aims: To describe prevalence and characteristics of iTTP Caucasian patients without anti-ADAMTS13-IgG-Ab detected by ELISA but with positive inhibition test and to better define the place of Bethesda assay for the diagnosis and follow-up of iTTP patients

Methods: We assessed ADAMTS13 activity with Technozym ADAMTS13 activity kit (Technoclone) and anti-ADAMTS13 IgG-Ab with Technozym ADAMTS13-INH ELISA kit (Technoclone). Inhibiting anti-ADAMTS13-Ig-Ab were detected after incubating heat-inactivated patient plasma with control plasma. Percentage of inhibition was calculated as the ratio between residual and expected activities. Positive inhibitory activity was considered as percentage of inhibition > 40%.

Results: - Between 1980 and 2023, 65 iPTT were diagnosed in our center (Table). For 6 patients (9%) no anti-ADAMTS13 IgG-Ab (negative ELISA) was detected while inhibitory activity was positive confirming iTTP. Four patients with negative ELISA and 19 with positive ELISA relapsed, totaling respectively 13 and 34 relapse episodes. Frequency of relapses were not different between the two groups, nevertheless, for negative ELISA patients, the number of relapses per patient is higher (p = 0.019) and relapses always occured with the same biological pattern.

Conclusion(s): These data confirm the place of the inhibition test to identify the immune nature of TTP and start the appropriate treatment. As relapses occur on the same way, regular monitoring should include Bethesda assay for theses patients