Prevalence of heparin/platelet factor 4 antibodies before and after cardiac surgery.

BACKGROUND: The clinical significance of heparin/platelet factor 4 (PF4) antibodies in subjects undergoing cardiac surgery has not been systematically studied. We prospectively investigated whether the presence of heparin/PF4 antibodies would predict clinical thrombosis in this population. METHODS: In 299 patients scheduled for cardiac surgery between October 2003 and March 2005, the heparin/PF4 antibodies and platelet count were measured immediately prior to, and 5 days after, surgery. The patients were followed up at 30 days for thrombotic complications. RESULTS: The prevalence of the heparin/PF4 antibodies was 4.3% (13 of 299) prior to surgery and increased more than fivefold to 22.4% (62 of 277) postoperatively (p < 0.0001). Thromboembolic events occurred in 8.8% of patients with negative antibody and in 6.3% of patients with positive antibody (p = 0.77). Of the 62 patients with positive heparin/PF4 antibodies postoperatively, 22 (35.5%) were treated with a nonheparin anticoagulant. There was a trend toward higher rates of thromboembolic events in subjects who were thrombocytopenic compared with those who were not (17.1% and 6.7%, respectively, p = 0.06), regardless of antibody status. Two out of 8 patients (25%) with both thrombocytopenia and a positive antibody (clinical heparin-induced thrombocytopenia [HIT]) suffered a thromboembolic event, compared with 17 of 222 (7.7%) without clinical HIT (p = 0.13). CONCLUSIONS: The high prevalence of antibodies to the heparin/PF4 complex after cardiac surgery and the low rate of thromboembolic complications in this population suggest that the antibody alone does not confer an increased risk of thrombotic complications. Monitoring for thrombocytopenia is recommended.

Prevalence of heparin-induced thrombocytopenia in patients undergoing cardiac catheterization.

BACKGROUND: Heparin is ubiquitously used in cardiac catheterization but predisposes to the development of heparin-induced thrombocytopenia. The objective was to examine prospectively the prevalence of anti-platelet factor 4 (PF4)/heparin antibodies and heparin-induced thrombocytopenia in the population undergoing cardiac catheterization. METHODS: This is a prospective study of 500 consecutive patients presenting for cardiac catheterization at our institution who were enrolled over the course of 1 year. Anti-PF4/heparin antibodies and concurrent platelet counts were measured at catheterization and 5 days thereafter. Thrombotic complications were assessed 30 days after the procedure via telephone interview. All patients presenting for cardiac catheterization at our institution were screened. Inclusion criteria were (a) males and nonpregnant females with age >18 years and (b) patients scheduled to undergo cardiac catheterization. Patients with a known history of heparin-induced thrombocytopenia, with documented bleeding or hypercoagulability, and those at high risk for bleeding were excluded. RESULTS: Of 500 patients, 15 (3%) had anti-PF4/heparin antibodies before catheterization. After catheterization, the prevalence of anti-PF4/heparin antibodies increased to 10.1% (36 of 357) of the patients. Overall rates of thrombotic complications were low (4 of 445, 0.9%) and did not correlate with anti-PF4/heparin antibody status. Patients with an initial positive test for anti-PF4/heparin antibodies were more likely to have prior coronary disease (73.3% vs 45.2%; P < .05). Patients who developed anti-PF4/heparin antibodies after catheterization were more likely to have increased length of stay (3.7 vs 2.4 days; P = .02). The platelet count at the time of catheterization was lower in the cohort of patients who developed the second positive anti-PF4/heparin antibody test versus patients without a second positive antibody test (mean values of 191,800/microL vs 222,300/microL; P = .008). CONCLUSIONS: The prevalence of antibodies to PF4/heparin is low in the population presenting for cardiac catheterization. However, a significant proportion of patients develop antibodies to PF4/heparin after a small exposure to heparin during catheterization. Clinically significant thrombotic complications were rare and did not correlate with antibody status.