OC 33.4 - Detection of platelet-activating antibodies associated with VITT by flow cytometry: an italian experience

Monday, July 11, 2022

11:30 AM – 11:45 AM

Location: ExCel Center, ICC Capital Suite Room 7&12

Presentation Format: In-Person

Presenting Author(s)

SS

Silvia Sorrentino

Technical biologist and Resident
Unità Malattie Emorragiche e Trombotiche, Fondazione Policlinico Universitario Agostino Gemelli IRCSS, Rome, Italy
Rome, Lazio, Italy

Co-Author(s)

FC

Francesca Cesari

Biologist
Dept Experimental and Clinical Medicine, University of Florence, AOU Careggi, Florence, Italy
Florence, Toscana, Italy
AG

AnnaMaria Gori

Professor
Dept Experimental and Clinical Medicine, University of Florence, AOU Careggi, Florence, Italy
Florence, Toscana, Italy
RD

Raimondo De Cristofaro, MD, PhD

Professor, Haemostasis and Thrombosis Center Director
1.Fondazione Policlinico Universitario A. Gemelli, IRCCS, Center for Hemorrhagic and Thrombotic Diseases and Haemophilia Center, Rome, Italy; 2. Catholic University, Translational Medicine and Surgery Department Rome, Italy
Roma, Lazio, Italy
BG

Betti Giusti

Professor
University of Florence, Department of Clinical and Applied Medicine
Florence, Toscana, Italy
AR

Angela A Rogolino

Biologist
Dept Experimental and Clinical Medicine, University of Florence, AOU Careggi, Florence, Italy
Florence, Toscana, Italy
ES

Elena Sticchi

researcher
Dept Experimental and Clinical Medicine, University of Florence, AOU Careggi, Florence, Italy
Florence, Toscana, Italy
ED

Erica De Candia

Professor
Catholic University of Sacred Heart, Translational Medicine and Surgery Department
Rome, Lazio, Italy
RM

Rossella Marcucci

Professor
Dept Experimental and Clinical Medicine, University of Florence, AOU Careggi, Florence, Italy
Florence, Toscana, Italy

Background: Rare cases of thrombocytopenia and thrombotic complications after adenoviral vaccination (VITT) caused by platelet activating anti-platelet factor 4 (PF4)/polyanions antibodies, have been reported. The laboratory diagnosis of VITT, similarly to the diagnosis of heparin induced thrombocytopenia (HIT), requires immunoassays for antibodies identification and platelet activating functional tests to confirm pathogenicity of anti-PF4/polyanions antibodies.

Aims: We compared flow cytometry (FC) measurement of p-selectin exposure and heparin-induced platelet activation test (HIPA) as functional tests to confirm VITT diagnosis in two Italian centers.

Methods: Anti-PF4/polyanions antibodies were assessed using immunoloassays (ELISA Lifecode PF4 IgG and Asserachrom HPIA-IgG assays; HemosIL AcuStar HIT-IgG (PF4-H) assay) and functional assays (FC measurement of p-selectin exposure in platelet rich plasma and HIPA in the presence of VITT samples + buffer/low/high heparin concentration.

Results: Thirteen VITT patients [6 M/7 F; median age 56 (33-78)] (Table 1) were all positive to ELISA and negative to AcuStar assays. Functional assay by FC identified three different patterns: 1) a typical VITT p-selectin exposure pattern in 7 patients showing platelet activation with buffer only, which was moderately reduced with low heparin and completely abolished with high heparin doses (Fig.1A); 2) 4 VITT patients investigated under IvIg therapy showed low or no platelet activation (Fig.1B); 3) a typical HIT pattern – platelet activation with low heparin dose abolished by high heparin dose- was found in 2 VITT patients (Fig.1C). The HIPA testing was positive in 11 VITT patients. Three patients were no more positive to both ELISA and FC analysis after 7, 17 and 24 days of therapy (Fig.1A).

Conclusion(s): FC measurement of P-selectin exposure was a simple and reliable method 1) to detect platelet-activating anti-PF4/polyanions antibodies in VITT patients, 2) to discriminate VITT from HIT, thus helping for the choise of the anticoagulant treatment, 3) to follow the response to therapies.