Temporal aspects of heparin-induced thrombocytopenia

Background: Heparin-induced thrombocytopenia is a relatively common antibod y-mediated drug reaction. We studied the temporal relation between previous or current heparin therapy and the onset of heparin-induced thrombocytopen ia. Methods: We examined the time between the start of heparin therapy and the onset of thrombocytopenia in 243 patients with serologically confirmed hepa rin-induced thrombocytopenia. We also investigated the persistence of circu lating heparin-dependent antibodies by performing a platelet serotonin-rele ase assay and an assay for antibodies against platelet factor 4. The outcom e in seven patients who had previously had an episode of heparin-induced th rombocytopenia and were later treated again with heparin was also examined. Results: A fall in the platelet count beginning four or more days after the start of heparin therapy occurred in 170 of the 243 patients (70 percent); in these patients, a history of previous heparin treatment did not influen ce the timing of the onset of thrombocytopenia. In the remaining 73 patient s (30 percent), the onset of thrombocytopenia was rapid (median time of ons et, 10.5 hours after the start of heparin administration); all these patien ts had been treated with heparin within the previous 100 days. During recov ery from thrombocytopenia, heparin-dependent antibodies in the serum fell t o undetectable levels at a median of 50 to 85 days, depending on the assay performed. In the seven patients who were given heparin again after the dis appearance of heparin-dependent antibodies, a new episode of heparin-induce d thrombocytopenia did not occur. Conclusions: Heparin-induced thrombocytopenia can begin rapidly in patients who have received heparin within the previous 100 days. Heparin-dependent antibodies do not invariably reappear with subsequent heparin use. (N Engl J Med 2001;344:1286-92.) Copyright (C) 2001 Massachusetts Medical Society.