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Plasma exchange to remove HIT antibodies: dissociation between enzyme-immunoassay and platelet activation test reactivities

Theodore E. Warkentin, Jo-Ann I. Sheppard, F. Victor Chu, Anil Kapoor, Mark A. Crowther and Azim Gangji

Key points

  • Repeated plasma exchange removes sufficient HIT-IgG to achieve negative serotonin-release assay (SRA) despite ongoing strong-positive EIA.

  • Serially-diluted HIT sera tested in both SRA and EIA show that SRA negativity can be achieved with minimal decrease in EIA reactivity.

Abstract

Repeated therapeutic plasma exchange (TPE) has been advocated to remove heparin-induced thrombocytopenia (HIT) IgG antibodies prior to cardiac/vascular surgery in patients who have serologically-confirmed acute or subacute HIT; for this situation, a negative platelet activation assay (e.g., platelet serotonin-release assay [SRA]) has been recommended as the target serological endpoint to permit safe surgery. We compared reactivities in the SRA and an anti-PF4/heparin IgG-specific enzyme-immunoassay (EIA), testing serial serum samples in a patient with recent (subacute) HIT who underwent serial TPE pre-cardiac surgery, as well as for 15 other serially-diluted HIT sera. We observed that post-TPE/diluted HIT sera—when first testing SRA-negative—continue to test strongly positive by EIA-IgG. This dissociation between the platelet activation assay and a PF4-dependent immunoassay for HIT antibodies indicates that patients with subacute HIT undergoing repeated TPE prior to heparin re-exposure should be tested by serial platelet activation assays even when their EIAs remain strongly positive.

  • Submitted July 23, 2014.
  • Accepted September 30, 2014.