Heparin–platelet factor 4 antibodies in patients presenting to the ED with thrombosis

Background Patients with heparin–platelet factor 4 (PF4) antibodies, particularly platelet-activating ones, are at risk for heparin-induced thrombocytopenia if administered heparin. We determined the heparin-PF4 antibody prevalence in emergency department (ED) patients presenting with chest pain or symptoms of thrombosis. Methods Admission samples from 324 ED patients with chest pain or symptoms of thrombosis were tested for heparin-PF4 antibodies and, if positive, platelet-activating antibodies. Results Twenty-four (7.4%; 95% confidence interval, 4.8%-10.8%) patients had heparin-PF4 antibodies. Seropositivity occurred in 18 (9.2%) of 196 patients recently (≤6 months) hospitalized vs 6 (4.7%) of 128 not recently hospitalized (P = .19), and in 16/231 (6.9%) patients with chest pain vs 8/93 (8.6%) with other thrombosis (P = .64). Of 22 seropositive patients retested, 8 (7 recently hospitalized) had platelet-activating antibodies. Conclusion Heparin-PF4 antibody prevalence is 7.4% in ED patients with chest pain or thrombosis, with 1 in 3 seropositive patients having platelet-activating antibodies. Alternative, nonheparin anticoagulation would be prudent in these at-risk patients.