title: Heparin resistance as detected with an antifactor Xa assay is not more common in venous thromboembolism than in other thromboembolic conditions.
abstract: OBJECTIVE
  To identify whether heparin resistance when measured with an antifactor Xa assay is more frequent in patients with venous thromboembolic disease than in patients with other thromboembolic conditions.
  
  
  METHODS
  Prospective observational cohort study.
  
  
  METHODS
  A 625-bed, adults-only, private teaching hospital.
  
  
  METHODS
  Three hundred seventy-two patients receiving intravenous unfractionated heparin for a variety of indications classified as either venous thromboembolism or arterial thromboembolism.
  
  
  METHODS
  All patients received an initial unfractionated heparin dosage according to a protocol based on age and estimated blood volume. Targeted antifactor Xa was 0.35-0.65 U/ml.
  
  
  RESULTS
  A modest increase in heparin dosage requirement was noted in patients with venous thromboembolism that was entirely related to lower hemoglobin concentration in that group compared with the arterial thromboembolism group. Low hemoglobin concentration was significantly associated with increased heparin resistance regardless of treatment indication.
  
  
  CONCLUSIONS
  True heparin resistance seen with an antifactor Xa assay is not more common in venous thromboembolism than in other conditions. Low hemoglobin concentration, rather than treatment indication, appears to be associated with increased heparin resistance.
authors.affiliation: Medical Education Department, Abbott Northwestern Hospital, Minneapolis, Minnesota 55407, USA. trosborough@mn.rr.com
authors.forename: Terry K
authors.initials: TK
authors.lastname: Rosborough
authors.forename: Michele E
authors.initials: ME
authors.lastname: Shepherd
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000008:administration & dosage* / Q000097:blood; D015331:Cohort Studies; D016903:Drug Monitoring / Q000379:methods*; D004351:Drug Resistance; D015951:Factor Xa / Q000032:analysis*; D005260:Female; D006493:Heparin / Q000008:administration & dosage* / Q000097:blood; D006801:Humans; D007262:Infusions, Intravenous; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013923:Thromboembolism / Q000188:drug therapy* / Q000473:pathology
chemical_list: D000925:Anticoagulants; D006493:Heparin; D015951:Factor Xa