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

ObjectiveApproximately 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.MethodsBlood 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.ResultsOf 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.ConclusionPatients 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.