Heparin-induced thrombocytopenia in patients treated with unfractionated heparin: Prevalence of thrombosis in a 1 year follow-up

BACKGROUND: Patients with unstable angina are usually treated with unfractionated heparin and aspirin, but very little is known about the prevalence of heparin-induced antibodies and their relation to thrombotic complications some time after the acute phase of unstable angina. The aim of the present study was to establish the prevalence of heparin-induced thrombocytopenia and the prevalence of heparin-dependent platelet-reactive antibodies in patients treated with unfractionated heparin and the occurrence of thrombosis in a 1 year follow-up. METHODS: Patient population included 124 consecutive patients with unstable angina treated with unfractionated heparin for almost 5 days. The prevalence of heparin-dependent platelet-reactive antibodies using an ELISA assay was measured before the beginning of heparin therapy and after 7 and 40 days. The platelet count was measured at the same time and the presence of thrombotic occurrences was checked. Clinical follow-up lasted 1 year. RESULTS: At baseline no one patient was positive for heparin-induced antibodies. On day 6, 38 patients (30%) produced a positive heparin-induced antibody result and 30 patients (24%) had an intermediate result. The majority of patients (74%) who developed antibodies became positive after 6 days of heparin therapy. The combined incidence of death, myocardial infarction, recurrent angina, urgent revascularization and stroke was 66% in patients with antibodies and 44% in patients without antibodies during a 1 year follow-up. The incidence of combined primary end points was statistically higher in patients positive for antibodies. The log-rank test was statistically significant (chi2 = 4.39, p < 0.01). CONCLUSIONS: No one patient developed a clinical evidence of thrombocytopenia. Nevertheless thrombotic events during follow-up were more common in patients who developed heparin-induced antibodies. These patients need a more accurate evaluation and surveillance after hospital discharge.

Background. Patients with unstable angina are usually treated with unfractionated heparin and aspirin, but very little is known about the prevalence of heparin-induced antibodies and their relation to thrombotic complications some time after the acute phase of unstable angina. The aim of the present study was to establish the prevalence of heparin-induced thrombocytopenia and the prevalence of heparin-dependent platelet-reactive antibodies in patients treated with unfractionated heparin and the occurrence of thrombosis in a 1 year follow-up. Methods. Patient population included 124 consecutive patients with unstable angina treated with unfractionated heparin for almost 5 days. The prevalence of heparin-dependent platelet-reactive antibodies using an ELISA assay was measured before the beginning of heparin therapy and after 7 and 40 days. The platelet count was measured at the same time and the presence of thrombotic occurrences was checked. Clinical follow-up lasted 1 year. Results. At baseline no one patient was positive for heparin-induced antibodies. On day 6, 38 patients (30%) produced a positive heparin-induced antibody result and 30 patients (24%) had an intermediate result. The majority of patients (74%) who developed antibodies became positive after 6 days of heparin therapy. The combined incidence of death, myocardial infarction, recurrent angina, urgent revascularization and stroke was 66% in patients with antibodies and 44% in patients without antibodies during a 1 year follow-up. The incidence of combined primary end points was statistically higher in patients positive for antibodies. The log-rank test was statistically significant (x2= 4.39, p < 0.01). Conclusions. No one patient developed a clinical evidence of thrombocytopenia. Nevertheless thrombotic events during follow-up were more common in patients who developed heparin-induced antibodies. These patients need a more accurate evaluation and surveillance after hospital discharge.