PB1083 - Accuracy Of The Hyphen Zymutest IgG ELISA Assay For Anti-Platelet Factor 4 Antibody Detection After ChAdOx1 nCov-19 Vaccination In Diagnosing Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT)

Tuesday, July 12, 2022

6:30 PM – 7:30 PM

Location: Exhibition

Presentation Format: In-Person

Presenting Author(s)

Emma Leitinger, MBBS BMedSci RCPA RACP

Haematology Fellow
Monash Health
Melbourne, Victoria, Australia

Co-Author(s)

JC

Joanne Clifford

Senior Laboratory Coagulation Scientist
Monash Health
Melbourne, Victoria, Australia
MP

Michael Parker

Scientist
Monash Health
Melbourne, Victoria, Australia
AI

Amanda Iacobelli

Scientist
Monash Health
Melbourne, Victoria, Australia
PS

Pauline Sung

Scientist
Monash Health
Melbourne, Victoria, Australia
VC

Vivien M. Chen, Phd FRACP FRCPA

Group Leader, Staff Specialist Haematologist
ANZAC Research Institute, University of Sydney
Sydney, New South Wales, Australia
TB

Timothy Brighton

Professor
Prince of Wales Hospital
Sydney, New South Wales, Australia
FP

Freda Passam

Group Leader
Haematology Research Group, Charles Perkins Centre, University of Sydney
Sydney, New South Wales, Australia
LC

Lisa Clarke

Consultant Haematologist
Department of Haematology, Concord Repatriation General Hospital; Australian Red Cross Lifeblood, Sydney Adventist Hospital
Concord, New South Wales, Australia
HT

Huyen Tran

Professor
Australian Centre for Blood Diseases, Monash University
Melbourne, Victoria, Australia
SC

Sanjeev Chunilal

Head of Laboratory, Head of Thrombosis and Haemostasis
Monash Health
Melbourne, Victoria, Australia

Background: Vaccine-induced Immune Thrombotic Thrombocytopenia (VITT) is a rare, anti-platelet factor 4 (PF4) antibody-mediated prothrombotic syndrome associated with the AstraZeneca (AZ) Covid-19 vaccination. Diagnostic criteria include thrombosis, thrombocytopenia, appropriate timing post AZ vaccine, and demonstration of an anti-PF4 antibody by enzyme-linked immunosorbent assay (ELISA). ELISA methods have varying sensitivity and specificity for detecting anti-PF4 antibodies, therefore, functional assays (modified serotonin release and flow cytometry) assist in diagnosis. In Australia, the primary assay for detection of anti-PF4 antibodies is the Asserachrom HPIA IgG ELISA.

Aims: To assess the accuracy of an alternate ELISA method for suspected VITT compared to the gold standard (clinicopathological diagnosis).

Methods: 96 stored frozen samples from patients with suspected VITT, previously analysed by Asserachrom HPIA IgG ELISA (Stago, Melbourne, Australia), were tested using the Hyphen Biomed Zymutest HIA IgG ELISA (Haematex Research, Sydney, Australia). These patients had confirmed thrombosis within 42 days post first dose of AZ vaccine. Cases were classified as ‘serologically confirmed VITT’ if clinicopathological criteria were met, and initial ELISA testing and/or functional assays were positive. Results were interpreted as positive or negative for anti-PF4 antibodies using the manufacturer’s cut-offs derived for the diagnosis of Heparin-Induced Thrombocytopenia.

Results: 96 patient samples were tested, including 35 classified as VITT (Table 1). The Hyphen assay had a moderate sensitivity (82%), including 2 probable false negatives on initial testing which were strongly positive by Hyphen assay. The specificity was 93%, including 5 probable false positives on initial ELISA which were negative by Hyphen assay (Table 2).

Conclusion(s): The Hyphen ELISA is suitably accurate for the diagnosis of VITT. These data highlight the limitations of using a single ELISA testing method for anti-PF4 antibody detection. In cases with high clinical suspicion, a second ELISA method or functional assay should be considered.