Persistence of heparin-dependent antiplatelet antibody

Heparin-induced thrombocytopenia is an immune-mediated response that has been associated with bleeding and thromboembolic complications. We test all cardiac surgery patients who experience thrombocytopenia, resistance to heparin, or have complications of increased bleeding or thrombosis with platelet aggregation assay for heparin-dependent antiplatelet antibody (HAAb). Due to the morbidity and mortality associated with reexposure to heparin in this population, we wished to investigate the length of time patients remain positive for HAAb postoperatively. Over a 10-year period (1982–1992), 97 patients tested positive for HAAb following open heart surgery. Of 66 survivors, 43 were available for follow-up and were contacted for repeat HAAb testing. Patients were retested from 1 to 126 months (median 17) postoperatively. Eleven of 43 patients (26%) remained positive for HAAb from 3 months to 12.5 years after initial diagnosis. Conversion from a positive to negative HAAb as early as 4 weeks was also observed. We conclude that the time to conversion to a negative HAAb test is highly variable. All patients who test positive for HAAb should have repeat HAAb testing before reexposure to heparin regardless of the time interval.