Abstract 1657: Heparin/PF4 Antibodies Formation after Heparin Treatment: Temporal Aspects and Long-Term Follow-Up
Heparin-induced thrombocytopenia (HIT) is an immunologic drug reaction characterized by the presence of heparin-induced antibodies against heparin-platelets factor4(PF4) complex, thrombocytopenia, and paradoxical thrombosis. Little information is available on the persistence of heparin/PF4 antibody complexes in the plasma.The aim of this study was to evaluate the time course of heparin/PF4 antibodies in patients (pts) exposed to heparin. We enrolled 500 pts treated with i.v. heparin as part of perioperative management of CABG, 131 of them developed serologically confirmed heparin/PF4 antibodies, and were then selected and followed-up. Serum concentration of circulating heparin-induced antibodies was repeatedly assessed over a period of 3 years by an ELISA immunoassay; we also evaluated occurrence of thrombotic events during follow-up. 131 of 500 pts (26.2%) developed anti-PF4/heparin antibodies which persisted for 90 days (median time 95%CI 80 to 156). Baseline platelet count did not differ between the antibody-positive and -negative groups, in contrast the nadir platelet count was significantly lower in antibody-positive pts (85.000 ± 21.000 vs 141.000 ± 41.000, p < 0.001).Pts with anti-PF4/heparin had higher incidence at 30 day of thrombotic events (28.2% vs 14.9%, p < 0.01), and death/MI (14.5% vs 7.8%, p < 0.001) than pts who were negative for the antibody. During the course of follow-up, thrombotic complications occurred in 57 pts (43%) with antibodies. Of the 131 pts with antibodies, 78 had already developed antibodies before CABG. Such pts became negative more slowly than the pts who developed antibodies only after CABG. The median time to negative test was 120 days (95%CI 100 to 156) in group with pre-existing antibodies vs 70 days (95%CI 65 to 114) in pts that developed antibodies after surgery. HIT is associated with a high rate of thrombosis in pts subjected to cardiac surgery. Pts having antibodies before cardiac surgery are more likely to develop thrombotic events. These pts also showed a greater persistence of antibodies over time. The long persistence of antibodies suggests that these pts may be at risk for developing thrombotic complication and additional heparin exposure had to be limited.