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Comment
. 2021 Jul 22;385(4):376-378.
doi: 10.1056/NEJMc2106383. Epub 2021 May 19.

PF4 Immunoassays in Vaccine-Induced Thrombotic Thrombocytopenia

Caroline Vayne  1 , Jérôme Rollin  1 , Yves Gruel  1 , Claire Pouplard  1 , Hubert Galinat  2 , Olivier Huet  2 , Vincent Mémier  3 , Thomas Geeraerts  3 , Raphael Marlu  4 , Gilles Pernod  4 , Guillaume Mourey  5 , Alexandra Fournel  6 , Charlotte Cordonnier  7 , Sophie Susen  7
Affiliations
Comment

PF4 Immunoassays in Vaccine-Induced Thrombotic Thrombocytopenia

Caroline Vayne et al. N Engl J Med. .
No abstract available

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Figures

Figure 1
Figure 1. PF4-Specific Immunoassays and SRA in Patients with Suspected VITT.
Panel A shows that rapid immunoassays do not detect antibodies to platelet factor 4 (PF4) associated with vaccine-induced immune thrombotic thrombocytopenia (VITT). All the plasma samples from the patients with findings suggestive of VITT were tested with two rapid immunoassays (STic Expert HIT, Stago, and HemosIL AcuStar HIT-IgG, Werfen), and negative results were obtained in every case. Two other rapid assays had also been performed in some patients (each represented by a specific symbol) in the referring centers (ID-PaGIA H/PF4, DiaMed, and HemosIL HIT-Ab, Werfen), and they also showed negative or doubtful (in patient *, who had an initial positive result but then tested negative) results. Panel B shows that the sensitivity of enzyme-linked immunosorbent assays (ELISAs) to detect PF4-specific IgG antibodies depends on the antigen target. Levels of PF4-specific IgG antibodies were evaluated in plasma samples from the nine patients with suspected VITT (each represented by a specific symbol) with the use of three different ELISAs with varying antigen targets (PF4–heparin complexes [Asserachrom HPIA, Stago], PF4 released from a platelet lysate [PL] and complexed with heparin [Zymutest HIA IgG, Hyphen], and PF4–poly[vinyl sulfonate] [PVS] complexes [Lifecodes PF4 IgG, Immucor]). OD denotes optical density. Panel C shows that a serotonin release assay (SRA) should be performed with the use of PF4 to detect platelet-activating antibodies to VITT. SRA was performed by incubating 75 μl of washed platelets obtained from healthy persons with 20 μl of plasma obtained from each patient, either in the absence (standard SRA) or the presence (PF4–SRA) of 10 μg per milliliter of PF4. All tests were performed with or without unfractionated heparin at 0.1 IU per milliliter (UFH 0.1), 0.5 IU per milliliter (UFH 0.5), and 10 IU per milliliter (UFH 10). Clinically significant and strong platelet activation, with maximum release ranging from 36 to 99%, was measured in seven of the nine patients only when PF4 was present in the reaction mixture. Moreover, platelet activation was not inhibited by therapeutic concentrations of UFH 0.1 or UFH 0.5. In contrast, platelet activation was completely abolished by 10 μg per milliliter of IV.3, a monoclonal antibody specific for FcγRIIA, or 6 U of IdeS, an IgG-degrading enzyme of Streptococcus pyogenes, preincubated for 15 minutes at 37°C in the plasma sample of each patient tested (five patients) before SRA.
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