title: Effect of distance to health facility on the maintenance of INR therapeutic ranges in rheumatic heart disease patients from Cape Town: no evidence for an association.
abstract: BACKGROUND
  Lack of adherence to international normalised ratio (INR) monitoring in rheumatic heart disease (RHD) patients is a contributor to cardio-embolic complications. This population-based observational study investigated whether the distance between home and an INR clinic affects the maintenance of therapeutic INR in RHD patients on warfarin.
  
  
  METHODS
  Residential addresses, INR clinics, and INR results of patients with RHD were extracted from the Cape Town component of the Global Rheumatic Heart Disease Registry (REMEDY) database. Addresses of homes and INR clinics were converted to geographical coordinates and verified in ArcGIS 10®. ArcGIS 10® and Google Maps® were used for spatial mapping and obtaining shortest road distances respectively. The travel distance between the home and INR clinic was correlated with time within therapeutic range (TTR) using the Rosendaal linear interpolation method, and with the fraction of INR within range, based on an average of three INR readings of patients and compared with recommended therapeutic ranges.
  
  
  RESULTS
  RHD patients (n = 133) resided between 0.2 km and 50.8 km (median distance, 3.60 km) from one of 33 INR clinics. There was no significant difference in the achievement of the therapeutic INR between patients who travelled a shorter distance compared to those who travelled a longer distance (in range = 3.50 km versus out of range = 3.75 km, p = 0.78). This finding was the same for patients with mechanical valve replacement (n = 105) (3.50 km versus 3.90 km, p = 0.81), and native valves (3.45 km versus 2.75 km, p = 0.84).
  
  
  CONCLUSIONS
  There is no association between the maintenance of INR within therapeutic range amongst RHD patients in Cape Town and distance from patients' residence to the INR clinic.
authors.affiliation: Department of Medicine, Groote Schuur Hospital and University of Cape Town, J46.43 Old Main Building, Private Bag, 7700, Rondebosch, South Africa.
authors.forename: Dylan D
authors.initials: DD
authors.lastname: Barth
authors.affiliation: Department of Medicine, Groote Schuur Hospital and University of Cape Town, J46.43 Old Main Building, Private Bag, 7700, Rondebosch, South Africa.|Department of Paediatrics, Red Cross War Memorial Children's Hospital and University of Cape Town, Cape Town, South Africa.
authors.forename: Liesl J
authors.initials: LJ
authors.lastname: Zühlke
authors.affiliation: Department of Medicine, Groote Schuur Hospital and University of Cape Town, J46.43 Old Main Building, Private Bag, 7700, Rondebosch, South Africa.
authors.forename: Alexia
authors.initials: A
authors.lastname: Joachim
authors.affiliation: Skiza Consulting Ltd., Cape Town, South Africa.
authors.forename: Tyler
authors.initials: T
authors.lastname: Hoegger
authors.affiliation: Department of Medicine, Groote Schuur Hospital and University of Cape Town, J46.43 Old Main Building, Private Bag, 7700, Rondebosch, South Africa.
authors.forename: Bongani M
authors.initials: BM
authors.lastname: Mayosi
authors.affiliation: Department of Medicine, Groote Schuur Hospital and University of Cape Town, J46.43 Old Main Building, Private Bag, 7700, Rondebosch, South Africa. mark.engel@uct.ac.za.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Engel
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000925:Anticoagulants / Q000627:therapeutic use; D005260:Female; D040362:Geographic Information Systems; D006268:Health Facilities; D006297:Health Services Accessibility; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D008875:Middle Aged; D012042:Registries; D012214:Rheumatic Heart Disease / Q000188:drug therapy*; D013019:South Africa; D014859:Warfarin / Q000627:therapeutic use; D055815:Young Adult
chemical_list: D000925:Anticoagulants; D014859:Warfarin