Abstract Number: PB0854
Meeting: ISTH 2021 Congress
Background: The diagnosis of Heparin-induced thrombocytopenia (HIT) often necessitates functional assays to demonstrate in vitro that antibodies to platelet factor 4 (PF4) are activating platelets, typically only in the presence of therapeutic heparin (H) concentrations (“classical” pattern). More rarely, HIT samples activate platelets even without heparin (“atypical” pattern). However, the clinical significance of such a profile is unclear.
Aims: We aimed to analyze the clinical and biological course of HIT patients according to their platelet activation pattern in serotonin release assay (SRA) and the main characteristics of PF4-specific antibodies.
Methods: We enrolled 74 patients with definite HIT under heparin treatment, and exhibiting in SRA either a “classical” (n=62), or “atypical” pattern (n=12). Titers of IgG to PF4/H complexes and PF4 alone were measured by ELISA in 41 selected patients, and results were analyzed according to the SRA pattern, and bioclinical features.
Results: Higher anti-PF4/H IgG titers were measured in patients with an “atypical” SRA (median OD 2.52 vs. 1.94 in those with a “classical” pattern, p< 0.001). Patients of both groups had similar platelet count (PC) nadir and time to recovery, but those with an “atypical” SRA developed more thrombotic events (66.7 vs. 33.9%, p= 0.05). Significant levels of anti-PF4 IgG (OD > 0.4) were detected in both groups (38% and 58%, respectively). But whatever the SRA pattern, a lower PC nadir (median: 30 vs. 54 G/L, p= 0.007) and a longer PC recovery time (median: 6 vs. 3 days, p= 0.01) were evidenced in patients with anti-PF4 antibodies, compared to those with anti-PF4/H IgG only.
Conclusions: An atypical SRA pattern with elevated anti-PF4/H IgG titers appears to be associated with an increased risk of thrombosis in HIT. IgG antibodies to PF4 alone may contribute to more severe and persistent thrombocytopenia, and their detection could be useful in clinical practice.
To cite this abstract in AMA style:Charuel N, Rollin J, Gruel Y, Guéry E-, May M-, Pouplard C, Vayne C. Variable Serotonin Release Assay Pattern and Characteristics of PF4-specific Antibodies in Heparin-Induced Thrombocytopenia, and Clinical Impact [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 2). https://abstracts.isth.org/abstract/variable-serotonin-release-assay-pattern-and-characteristics-of-pf4-specific-antibodies-in-heparin-induced-thrombocytopenia-and-clinical-impact/. Accessed December 5, 2021.
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