The effect of a heparin removal filter on platelet aggregation studies in heparin-induced thrombocytopenia

Patients having a heparin-associated platelet antibody who are receiving heparin at the time of testing for heparin-induced thrombocytopenia (HIT) by platelet aggregometry may exhibit aggregation in the negative control channel. Filtering plasma to remove the heparin in may produce a nonaggregating negative control channel. The effect of the Pall Hepchek (Pall Biomedical, East Hills, NY) heparin removal filter on platelet aggregation studies was evaluated. Samples were studied from 10 patients with clinically established HIT. The pre-filtration platelet aggregation studies were unequivocally positive for heparin antibody. The remainder of each sample was filtered and the aggregation studies were repeated. Of the four patients on IV heparin, only one remained positive post-filtration. Of the six patients receiving subcutaneous heparin or flushes, one remained strongly positive, one was borderline, and four became negative. Pall Hepchek heparin filtration unpredictably alters the results of platelet aggregation studies, and should not be used routinely to remove heparin in the presence of aggregation in the negative control.