PB0326 - Rapid immunoassay for platelet factor-4 in the diagnosis of vaccine-induced immune thrombotic thrombocytopenia after vaccination with ChAdOx1 nCoV-19

Sunday, July 10, 2022

6:30 PM – 7:30 PM

Location: Exhibition

Presentation Format: In-Person

Presenting Author(s)

Günalp Uzun, MD

Physician
Center for Clinical Transfusion Medicine, University Hospital of Tübingen
Tübingen, Baden-Wurttemberg, Germany

Co-Author(s)

Karina Althaus, MD

Physician, Director of Platelet Immunology Lab.
Center for Clinical Transfusion Medicine, University Hospital of Tübingen
Tübingen, Baden-Wurttemberg, Germany
Stefanie Hammer, MD

Physician
Center for Clinical Transfusion Medicine
Tübingen, Baden-Wurttemberg, Germany
YW

Yvonne Wanner

Doctor
Center for Clinical Transfusion Medicine
Tuebingen, Baden-Wurttemberg, Germany
SN

Stefanie Nowak-Harnau

Physician
Center for Clinical Transfusion Medicine
Tübingen, Baden-Wurttemberg, Germany
SE

Sigrid Enkel

Doctor
Center for Clinical Transfusion Medicine
Tuebingen, Baden-Wurttemberg, Germany
Tamam Bakchoul, MD

Medical Director
Center for Clinical Transfusion Medicine, University Hospital of Tübingen
Tübingen, Baden-Wurttemberg, Germany

Background: Vaccine-induced immune thrombotic thrombocytopenia (VITT) is characterized by the presence of platelet activating antibodies against platelet factor 4 (PF-4). The prompt diagnosis is of paramount importance in the management of VITT. First step in the laboratory diagnosis of VITT is the detection of anti-PF4 antibodies. Although recently published expert opinions recommend against the use of rapid immunoassays, their diagnostic performance have not been investigated systematically before.

Aims: To evaluate the performance of rapid immune assay in the dignosis of VITT.

Methods: In this retrospective single-center study, we evaluated the correlation between rapid immunoassay, enzyme-linked immunosorbent assay (ELISA) and modified heparin induced platelet aggregation assay (HIPA) in patients with findings suggestive of VITT. A commercially available PF4 rapid immunoassay (ID PaGIA H/PF4, Diamed) and an anti PF4/Heparin ELISA (Zymutest HIA IgG, Hyphen) were used according to manufacturer´s instructions. A sample was considered reactive in ELISA if the optical density (OD) was ≥0.500. Modified HIPA was accepted as the gold standard test.

Results: Between March 8th and May 20th, 21 samples from clinically well-characterized VITT patients were analyzed with PF4 rapid immunoassay. Of these sera 8 revealed positive results and 13 tested negative in rapid immunoassay. In contrast, all sera showed positive results in ELISA and modified HIPA. Sensitivity and specificity of rapid immunoassay were 50% and 69%, respectively. On the other hand, sensitivity and specificity of ELISA were 88% and 92%, respectively.

Conclusion(s): Particle gel immunoassay is not reliable in the detection of anti-PF4 antibodies in patients suspected of VITT.