THROMBOEMBOLISM PROPHYLAXIS AS A CAUSE OF THROMBOEMBOLIC COMPLICATIONS - AN INVESTIGATION INTO THE INCIDENCE OF HEPARIN-INDUCED THROMBOCYTOPENIA (HIT) TYPE-II

Problem: A life-threatening complication of the thrombembolism prophyl axis with heparin is heparin-induced thrombocytopenia (HIT) type II. H IT type II is based on immunological mechanisms. Even low, subcutaneou sly applied doses may produce HIT type II. In those patients, continue d application may cause thromboembolic complications. The most importa nt symptom of HIT type II is a decrease of platelets. Methods: In a pr ospective study, we investigated the incidence of HIT type II within t he period from 01. 07. 95 to 30. 06. 96 in orthopedic patients. We als o evaluated the importance of the daily platelet count from the fifth postoperative day for the early diagnosis of HIT type II and a possibl e reduction of the thrombosis rate. The study included 307 patients af ter primary implantation of hip and knee endoprosthesis and after hip endoprosthesis replacement. All patients received 3 x 5000 IU/d of unf ractionated heparin subcutaneously. Whenever there was a decrease of p latelets of at least 50% in relation to the preoperative value or when ever thrombembolic complications occurred, serum was analyzed by the h eparin-induced platelet activation test (HIPA). Results: 20 patients d eveloped HIT type II. This corresponds to an incidence of 6.5%. 10 of the HIT type II antibody positive patients (50%) developed thrombembol ic complications. 3 patients (0.9%) of the group studied developed cli nically symptomatic thrombembolic complications without evidence of he parin antibodies. The total risk of getting thrombembolic complication s was 4.2% (13 patients). 3.3% (10 patients) of the entire group devel oped HIT type II antibody associated thrombembolic complications; 1 pa tient died. The lethality in the HIT type II antibody positive patient group amounted to 5%. The patients with HIT type II received LMW hepa rinoid Orgaran(R) (AKZO-Organon, The Netherlands) or hirudin (as a cli nical trial). The comparison group (retrospective study from 17. 10. 9 2 to 16. 10. 93) was composed of 262 patients with the same operations and equal thromboembolism prophylaxis. The platelet count was made on ly as part of routine diagnostic tests. 21 patients (8.0%) developed c linically symptomatic thrombembolic complications. The difference in t he thrombosis rate between these two groups of patients is statistical ly significant. Unrecognized HIT type II is probably the reason for th e high thrombembolic complication rate in the comparison group. Conclu sions: The daily platelet count from the fifth postoperative day and f rom the first day in case of reexposure to heparin is an important mea sure for the early diagnosis of HIT type II.