Antiphospholipid syndrome, antiphospholipid antibodies, and stroke.

Antiphospholipid syndrome (APS) is a prothrombotic autoimmune disease with heterogeneous clinicopathological manifestations and is a well-established cause of acute ischemic stroke (AIS) and transient ischemic attack (TIA), particularly in younger patients. There is growing recognition of a wider spectrum of APS-associated cerebrovascular lesions, including white matter hyperintensities, cortical atrophy, and infarcts, which may have clinically important neurocognitive sequalae. Diagnosis of APS-associated AIS/TIA requires expert review of clinical and laboratory information. Management poses challenges, given the potential for substantial morbidity and recurrent thrombosis, additional risk conferred by conventional cardiovascular risk factors, and limited evidence base regarding optimal antithrombotic therapy for secondary prevention. In this review, we summarize key features of APS-associated cerebrovascular disorders, with focus on clinical and laboratory aspects of diagnostic evaluation. The current status of prognostic markers is considered. We review the evidence base for antithrombotic treatment in APS-associated stroke and discuss uncertainties, including the optimal intensity of anticoagulation and efficacy of direct oral anticoagulants. Clinical practice recommendations are provided, covering antithrombotic treatment, supportive management, and options for anticoagulant-refractory cases, and we highlight the benefits of adopting a considered, multidisciplinary team approach.

Platelet-activating functional assay resolution in vaccine-induced immune thrombotic thrombocytopenia: differential alignment to PF4 ELISA platforms.

Background: Anti-platelet factor 4 (PF4) antibodies in vaccine-induced immune thrombotic thrombocytopenia (VITT) appear to be transient, with discrepant persistence depending on the platform used for detection. Objectives: We aimed to report a longitudinal study of antibody persistence using 2 ELISA platforms and 2 platelet-activating functional assays in a clinical cohort of patients with VITT referred for follow-up testing. Methods: In total, 32 Australian patients with VITT or pre-VITT, confirmed by expert adjudication, with samples referred for clinical follow-up were included. Clinical follow-up assays, including Stago and Hyphen ELISAs, procoagulant platelet flow cytometry, and modified PF4-serotonin-release assay, were performed according to the pattern of reactivity for that patient at diagnosis. Results: The median follow-up was 24 weeks after diagnosis. A general decline in anti-PF4 antibody levels and platelet-activating capacity over time was observed with a more rapid median time to resolution of 16 weeks by functional assay vs 24 weeks by Stago ELISA. Decline in platelet-activating antibody levels detected by functional assays mirrored Stago ELISA titer but not Hyphen. However, 87% of patients received a documented second vaccination and 74% received an mRNA booster with no reported adverse events. Conclusion: Anti-PF4 antibodies persist longer than functional platelet-activating antibodies in VITT but do not warrant avoidance of subsequent vaccinations. Persistence detection is assay-dependent. Stago ELISA may be a surrogate where functional assays are unavailable for follow-up testing of confirmed patients with VITT.

A novel flow cytometry procoagulant assay for diagnosis of vaccine-induced immune thrombotic thrombocytopenia.

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a severe prothrombotic complication of adenoviral vaccines, including the ChAdOx1 nCoV-19 (Vaxzevria) vaccine. The putative mechanism involves formation of pathological anti-platelet factor 4 (PF4) antibodies that activate platelets via the low-affinity immunoglobulin G receptor FcγRIIa to drive thrombosis and thrombocytopenia. Functional assays are important for VITT diagnosis, as not all detectable anti-PF4 antibodies are pathogenic, and immunoassays have varying sensitivity. Combination of ligand binding of G protein-coupled receptors (protease-activated receptor-1) and immunoreceptor tyrosine-based activation motif-linked receptors (FcγRIIa) synergistically induce procoagulant platelet formation, which supports thrombin generation. Here, we describe a flow cytometry-based procoagulant platelet assay using cell death marker GSAO and P-selectin to diagnose VITT by exposing donor whole blood to patient plasma in the presence of a protease-activated receptor-1 agonist. Consecutive patients triaged for confirmatory functional VITT testing after screening using PF4/heparin ELISA were evaluated. In a development cohort of 47 patients with suspected VITT, plasma from ELISA-positive patients (n = 23), but not healthy donors (n = 32) or individuals exposed to the ChAdOx1 nCov-19 vaccine without VITT (n = 24), significantly increased the procoagulant platelet response. In a validation cohort of 99 VITT patients identified according to clinicopathologic adjudication, procoagulant flow cytometry identified 93% of VITT cases, including ELISA-negative and serotonin release assay-negative patients. The in vitro effect of intravenous immunoglobulin (IVIg) and fondaparinux trended with the clinical response seen in patients. Induction of FcγRIIa-dependent procoagulant response by patient plasma, suppressible by heparin and IVIg, is highly indicative of VITT, resulting in a sensitive and specific assay that has been adopted as part of a national diagnostic algorithm to identify vaccinated patients with platelet-activating antibodies.