title: A 14-year study of heparin-induced thrombocytopenia.
abstract: OBJECTIVE
  To determine the sites of thromboses (venous versus arterial circulation) that complicate the clinical course of immunemediated heparin-induced thrombocytopenia, and to determine the 30-day risk for thrombosis in patients who are initially recognized with isolated heparin-induced thrombocytopenia.
  
  
  METHODS
  We analyzed objectively documented thrombotic events that complicated the clinical course of 127 patients with serologically confirmed heparin-induced thrombocytopenia identified in one medical community over a 14-year period. We classified heparin-induced thrombocytopenia patients into two groups: patients recognized with heparin-induced thrombocytopenia only after a new thrombosis had occurred, and patients initially recognized with isolated heparin-induced thrombocytopenia. We determined the subsequent 30-day risk for thrombosis for the cohort of patients initially recognized with isolated thrombocytopenia.
  
  
  RESULTS
  Heparin-induced thrombocytopenia was associated with the development of new venous thrombotic events and arterial thrombotic events in 78 and 18 patients, respectively (ratio venous/arterial thrombosis = 4:1). Pulmonary embolism was the most common life-threatening thrombotic event, occurring in 25% of all patients. Approximately half of all heparin-induced thrombocytopenia patients were recognized only after they had a complicating thrombotic event. Of the remaining 62-patient cohort initially recognized with isolated thrombocytopenia, the subsequent 30-day risk of thrombosis was 52.8%. The risk of thrombosis did not differ whether the heparin had been discontinued alone or whether warfarin had been substituted for the heparin.
  
  
  CONCLUSIONS
  Venous thrombosis complicates heparin-induced thrombocytopenia more frequently than does arterial thrombosis. The high risk of thrombosis in patients initially recognized with isolated thrombocytopenia suggests that conventional management approaches require reappraisal.
authors.affiliation: Department of Laboratory Medicine, Hamilton Civic Hospitals (General Division), Ontario, Canada.
authors.forename: T E
authors.initials: TE
authors.lastname: Warkentin
authors.forename: J G
authors.initials: JG
authors.lastname: Kelton
mesh_terms: D000368:Aged; D000925:Anticoagulants / Q000009:adverse effects*; D005260:Female; D006493:Heparin / Q000009:adverse effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012306:Risk; D013921:Thrombocytopenia / Q000139:chemically induced*; D013927:Thrombosis / Q000209:etiology; D016896:Treatment Outcome
chemical_list: D000925:Anticoagulants; D006493:Heparin