Incidence and clinical relevance of anti–platelet factor 4/heparin antibodies before cardiac surgery

BACKGROUND: Heparin-induced thrombocytopenia (HIT) is caused by anti-platelet factor 4/heparin (PF4/H) immunoglobulin (Ig) G antibodies, which activate platelets. In some patients, anti-PF4/H antibodies are already detectable before cardiac surgery. Whether preoperative presence of antibodies confers adverse prognosis and which particular antibody classes (IgG, IgA, IgM) might be implicated are unknown. METHODS: We prospectively screened 591 patients undergoing cardiopulmonary bypass surgery for heparin-dependent antibodies by PF4/H immunoassay (separately for IgG, IgA, and IgM) and platelet activation test at preoperative baseline and at days 6 and 10. All patients received heparin or low-molecular-weight heparin postsurgery regardless of antibody status and were followed for postoperative complications, frequency of HIT, length of hospital stay, and 30-day mortality. RESULTS: Anti-PF4/H antibodies of any class were detected at preoperative baseline in 128 (21.7%) of 591 patients: IgG n = 44 (7.4%), IgA n = 36 (6.1%), and IgM n = 79 (13.4%); some patients had >1 antibody class. Neither IgG nor IgA was a risk factor for any adverse outcome parameter. However, preoperative presence of IgM antibodies was associated with an increased risk for nonthromboembolic complications (all complications combined: hazard ratio 1.73, 95% CI 1.15-2.61) and a longer in-hospital stay (P = .02), but without evidence for increased risk of thrombotic complications or subsequent HIT. CONCLUSIONS: Patients with preoperative anti-PF4/H antibodies of IgG and IgA class are not at increased risk for thrombotic or nonthrombotic adverse events, whereas those with baseline anti-PF4/H IgM had an increased risk of nonthrombotic adverse outcomes but not of subsequent HIT or thrombosis. Because IgM antibodies do not cause HIT, they could represent a surrogate marker for other heparin-independent risk factors.