PF4 Immunoassays in Vaccine-Induced Thrombotic Thrombocytopenia

This correspondence evaluates platelet factor 4 (PF4) immunoassay performance in diagnosing vaccine-induced immune thrombotic thrombocytopenia (VITT) after ChAdOx1 nCoV-19 vaccination. Plasma samples from nine patients with suspected VITT underwent testing with multiple PF4-specific enzyme-linked immunosorbent assays (ELISAs) and serotonin release assays. Seven patients had significant PF4-specific IgG antibodies detected only by PF4-poly(vinyl sulfonate) ELISA. Platelet activation was confirmed by PF4-enhanced serotonin release assay and suppressed by monoclonal antibody IV.3 and IgG-cleaving enzyme IdeS. Standard rapid PF4 assays yielded negative or equivocal results, emphasizing the need for sensitive, quantitative testing protocols. The findings support refined diagnostic algorithms for VITT and suggest IdeS may be a promising treatment.

This correspondence evaluates platelet factor 4 (PF4) immunoassay performance in diagnosing vaccine-induced immune thrombotic thrombocytopenia (VITT) after ChAdOx1 nCoV-19 vaccination. Plasma samples from nine patients with suspected VITT underwent testing with multiple PF4-specific enzyme-linked immunosorbent assays (ELISAs) and serotonin release assays. Seven patients had significant PF4-specific IgG antibodies detected only by PF4-poly(vinyl sulfonate) ELISA. Platelet activation was confirmed by PF4-enhanced serotonin release assay and suppressed by monoclonal antibody IV.3 and IgG-cleaving enzyme IdeS. Standard rapid PF4 assays yielded negative or equivocal results, emphasizing the need for sensitive, quantitative testing protocols. The findings support refined diagnostic algorithms for VITT and suggest IdeS may be a promising treatment.