A multicentre assessment of contemporary laboratory assays for heparin induced thrombocytopenia

The complicated relationships of heparin‐induced thrombocytopenia and platelet factor 4 antibodies with COVID‐19

“…This represents a functional event detected by functional assays, such as SRA (serotonin release assay) and HIPA (heparin‐induced platelet aggregation) 22,23 . Only a small proportion of detected PF4/H antibodies will cause platelet activation, and thus “positivity” in the functional assays, and therefore, the anticipated pathological consequence of thrombosis 21,24 . There is also an association between the level of detected PF4/H antibodies and the likelihood of “positivity” in a functional assay.…”

“…There is also an association between the level of detected PF4/H antibodies and the likelihood of “positivity” in a functional assay. For example, an ELISA OD >1.0 or a CLIA value >10 U/mL may be characterized as more likely associated with functional assay positivity 18,20,21,24 . However, it is generally accepted that a functional assay is required to confirm pathological HIT in a patient with immunologically detected PF4/H antibodies.…”

“…It needs to be noted that in non‐COVID‐19 literature, many patients may be found to have PF4/H antibodies, but most of these will not develop pathological HIT 56 . Moreover, a high level of PF4/H antibodies (especially as detected by ELISA) will not be positive by a functional assay such as SRA 20,24 …”

The first known case of vaccine‐induced thrombotic thrombocytopenia in Australia

“…Antibodies to the heparin–platelet factor 4 (PF4) complex in the patient’s plasma was strongly positive (optical density, 1.94) by enzyme‐linked immunosorbent assay (ELISA)‐based test (Asserachrom HPIA IgG; Stago). Three functional assays, including serotonin release assay (SRA; Hidex 300 SL, Hydex), multiple electrode aggregometry (MEA; Roche Diagnostics) and flow cytometry (BD Fortessa, ETH Zürich; procoagulant assay) all detected heparin‐independent PF4 antibody complexes that activated donor platelets 1 …”

Plasma vs serum as test sample for the chemiluminescent AcuStar HemosIL HIT‐IgG(PF4‐H) assay

“…5 We recently reported on our experience with this assay 6,7 ; with external collaborators, a multicenter study 7 identified the assay to provide excellent screening for the presence of pathological HIT antibodies, with high association to results of a surrogate gold-standard functional assay for pathological HIT, namely serotonin release assay; SRA. 7 This has also been recently shown by others, as summarized in review form, 4 and also in an original report. 8 As this methodology increases in usage, we wish to update readers on our experience with use of plasma vs serum as the sample for analysis.…”