title: Relation between quality of anticoagulant treatment and the development of the postthrombotic syndrome.
abstract: BACKGROUND
  About 30% of patients with an episode of adequately treated deep venous thrombosis (DVT) develop the postthrombotic syndrome (PTS) within 2 years. During treatment with vitamin K antagonists (VKA) patients spend only 60% of time between an International Normalized Ratio (INR) of 2.0 and 3.0. We hypothesized that patients who spend a large amount of their time beneath this range will have an increased risk of the PTS.
  
  
  OBJECTIVE
  To investigate the relation between the quality of anticoagulant therapy with VKA and the risk of the development of the PTS.
  
  
  METHODS
  The time spent beneath the therapeutic range was calculated for patients with a first episode of DVT, who were treated with VKA for at least 3 months. At follow-up assessments for a maximum of 5 years, presence and severity of signs and symptoms of PTS were recorded.
  
  
  RESULTS
  A total of 244 patients, with a median duration of follow-up of 4.9 years were included for analysis. Of these, 81 patients (33%) developed the PTS. The multivariate model showed that patients who spend more than 50% of their time beneath an INR level of 2.0 are at higher risk for PTS [odds ratio (OR): 2.71, 95% CI: 1.44-5.10].
  
  
  CONCLUSIONS
  Low quality treatment with VKA, which is a common condition, is related to the occurrence of the PTS in patients with DVT. Strategies aimed at improving the quality of long-term anticoagulation might have the potential to reduce the incidence of this complication.
authors.affiliation: Department of Clinical Epidemiology and Biostatistics, Academic Medical Center, Amsterdam, Netherlands. c.j.vandongen@amc.uva.nl
authors.forename: C J J
authors.initials: CJ
authors.lastname: van Dongen
authors.forename: P
authors.initials: P
authors.lastname: Prandoni
authors.forename: M
authors.initials: M
authors.lastname: Frulla
authors.forename: A
authors.initials: A
authors.lastname: Marchiori
authors.forename: M H
authors.initials: MH
authors.lastname: Prins
authors.forename: B A
authors.initials: BA
authors.lastname: Hutten
mesh_terms: D000368:Aged; D000925:Anticoagulants / Q000494:pharmacology*; D001458:Bandages; D002986:Clinical Trials as Topic; D015331:Cohort Studies; D005260:Female; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009369:Neoplasms / Q000150:complications; D016017:Odds Ratio; D011186:Postphlebitic Syndrome / Q000517:prevention & control*; D011786:Quality Control; D012189:Retrospective Studies; D012306:Risk; D013997:Time Factors; D020246:Venous Thrombosis / Q000188:drug therapy*; D014812:Vitamin K / Q000037:antagonists & inhibitors*
chemical_list: D000925:Anticoagulants; D014812:Vitamin K