title: Implications of using different methods to characterise anticoagulant control in patients with second generation mechanical heart valve prostheses.
abstract: OBJECTIVE
  Characterisation of anticoagulant control is fundamental to investigations of its association with clinical outcome. Anticoagulant control depends on several factors. This paper aims to illustrate the implications of different methods for measuring and analysing anticoagulant control in patients with second generation mechanical heart valve prostheses.
  
  
  METHODS
  International normalised ratio (INR) data collected during the 10-year follow-up of a randomised controlled trial were analysed. We considered the influence of: 3 different target INR ranges; anticoagulant control expressed as the proportion of INR readings (PoR) vs. anticoagulant control follow-up time (PoT); 3 ways of describing the profile of anticoagulant control over time.
  
  
  RESULTS
  Different target INR ranges dramatically influenced derived measures of anticoagulant control; the PoT within the target range varied from 88% for the widest to 28% for narrowest range. Overall distributions of PoR and PoT observations were similar but differed by up to ± 20% for individuals; PoT exceeded PoR when control was good but was less than PoR when control was poor. Classifying PoT outside the target range showed that widely varying combinations of PoT too high and too low are possible across individuals.
  
  
  CONCLUSIONS
  Researchers' choices about methods for measuring and quantifying anticoagulant control markedly influence the values derived from INR readings. The use of different methods across studies makes it difficult or impossible to compare findings and to establish an evidence base for clinical practice. Methods for quantifying anticoagulant control should be standardised.
authors.affiliation: National Heart & Lung Institute, Imperial College London, Hammersmith Hospital, London, United Kingdom.
authors.forename: Francesca
authors.initials: F
authors.lastname: Fiorentino
authors.affiliation: Bristol Heart Institute, University of Bristol, Bristol Royal Infirmary, Bristol, United Kingdom.
authors.forename: Chris A
authors.initials: CA
authors.lastname: Rogers
authors.affiliation: Bristol Heart Institute, University of Bristol, Bristol Royal Infirmary, Bristol, United Kingdom.
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Bryan
authors.affiliation: Bristol Heart Institute, University of Bristol, Bristol Royal Infirmary, Bristol, United Kingdom; National Heart & Lung Institute, Imperial College London, Hammersmith Hospital, London, United Kingdom.
authors.forename: Gianni D
authors.initials: GD
authors.lastname: Angelini
authors.affiliation: Bristol Heart Institute, University of Bristol, Bristol Royal Infirmary, Bristol, United Kingdom.
authors.forename: Barnaby C
authors.initials: BC
authors.lastname: Reeves
mesh_terms: D000925:Anticoagulants / Q000032:analysis* / Q000627:therapeutic use; D001021:Aortic Valve; D002986:Clinical Trials as Topic; D005500:Follow-Up Studies; D006350:Heart Valve Prosthesis; D006801:Humans; D019934:International Normalized Ratio; D008943:Mitral Valve; D013923:Thromboembolism / Q000517:prevention & control; D013927:Thrombosis / Q000517:prevention & control
chemical_list: D000925:Anticoagulants