A prospective study on the incidence and clinical relevance of heparin-induced antibodies in patients after vascular surgery

The heparin-platelet factor 4-antibody assay, polyanion-platelet factor 4-a ntibody assay and heparin-induced platelet activation test are used for lab oratory diagnosis of the immune form of heparin-induced thrombocytopenia. F ifty consecutive patients receiving heparin treatment for more than 5 days after vascular surgery were prospectively screened for heparin-induced thro mbocytopenia antibodies, thrombocytopenia (daily platelet counts), deep-vei n thrombosis (color-coded duplex sonography), and arterial reocclusion (cli nical assessment). None of the patients developed thrombocytopenia or throm bosis in association with formation of heparin-induced thrombocytopenia ant ibodies. Despite the absence of clinical evidence of heparin-induced thromb ocytopenia, many patients formed heparin-induced thrombocytopenia antibodie s: 34% of the patients were positive in the heparin-platelet factor 4-antib ody assay, 28% in the polyanion-platelet factor 4-antibody assay, 14% in th e heparin-induced platelet activation test, and 54% with any of these tests . Patients predominantly developed IgM (24%) and IgA antibodies (16%), wher eas IgG antibodies were found in 12% of patients. Whereas the majority of p atients with positive ELISA assays had IgM and IgA antibodies, patients wit h a positive functional assay (heparin-induced platelet activation test) pr edominantly had IgG antibodies. We conclude that a high percentage of patie nts develop heparin-induced antibodies after vascular surgery without any c linical symptoms of heparin-induced thrombocytopenia. None of the assays th erefore is predictive of the clinical manifestation of heparin-induced thro mbocytopenia in asymptomatic patients. Therefore, the diagnostic specificit y of both antigen and activation assays for heparin-induced thrombocytopeni a appears to be relatively low in the vascular surgery patient population. (C) 2000 Elsevier Science Ltd. All rights reserved.