Heparin-platelet factor 4 antibodies are frequent after vascular surgery but are not a frequent cause of graft thrombosis or thrombocytopenia

Objective: Approximately 10% of infrainguinal bypass surgeries are complicated by early conduit failure. The cause is unclear in most cases. A prospective study was conducted to monitor the development and function of platelet factor 4 (PF4)/heparin antibodies after infrainguinal bypass procedures and to evaluate their clinical significance in early graft occlusion. Methods: Blood samples were obtained before surgery and at the 7-, 14-, and 28-day postsurgical evaluation. Relevant demographic and laboratory data were collected, and plasma samples were assayed for the presence and function of PF4/heparin-antibody by enzyme-linked immunosorbent assay (ELISA) and a two-point platelet aggregation assay. All tests were performed in duplicate or triplicate. Results: Of the 79 patients who were enrolled, 67 reported previous heparin exposure. Six patients (7.6%) tested positive for the presence of PF4/heparin antibodies before surgery with ELISA, and four of these (67%) also had a positive result on the aggregation assay. During the 28-day follow-up, 22 subjects (32%) converted to positive according to the ELISA results; and five (22.7%) of these also tested positive for platelet-activating antibodies. No participants presented with thrombocytopenia or a ≥50% decrease in platelet count during the study period. Early graft occlusion was detected in three patients, all with negative ELISA and functional assay results throughout the study. Conclusion: Patients undergoing vascular surgery frequently develop PF4/heparin antibodies, with platelet-activating antibodies detected in up to 11% of these individuals. However, thrombocytopenia and vascular graft thrombosis both appear to be an uncommon consequence.