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

[heparin-induced thrombocytopenia]

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-PF 4 /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 PF 4 -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 .