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Research ArticleResearch

Quality of warfarin management in primary care

Determining the stability of international normalized ratios using a nationally representative prospective cohort

Sharon Liu, Alexander Singer, Finlay A. McAlister, William Peeler, Balraj S. Heran, Neil Drummond, Donna P. Manca, G. Michael Allan, Christina Korownyk, Michael R. Kolber, Michelle Greiver and Scott R. Garrison
Canadian Family Physician June 2019; 65 (6) 416-425;
Sharon Liu
Medical student in the Faculty of Medicine at the University of Alberta in Edmonton.
MB BCh BAO CCFP
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Alexander Singer
Family physician, Associate Professor in the Department of Family Medicine at the University of Manitoba in Winnipeg, and Director of the Manitoba Primary Care Research Network.
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Finlay A. McAlister
Professor in the Division of General Internal Medicine at the University of Alberta and lead for the Alberta SPOR (Support for Patient Oriented Research) Data Platform.
MD MSc
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William Peeler
Data Manager with the Manitoba Primary Care Research Network.
PhD
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Balraj S. Heran
Research Associate with the Therapeutics Initiative in the Department of Anesthesiology, Pharmacology, and Therapeutics at the University of British Columbia in Vancouver.
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Neil Drummond
Professor and holds the Alberta Health Services Chair in Primary Care Research in the Department of Family Medicine at the University of Alberta.
PhD
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Donna P. Manca
Director of Research in the Department of Family Medicine Research Program at the University of Alberta.
MD MClSc CCFP FCFP
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G. Michael Allan
Family physician, Director of Programs and Practice Support at the College of Family Physicians of Canada, and Professor in the Department of Family Medicine at the University of Alberta.
MD CCFP
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Christina Korownyk
Family physician and Associate Professor in the Department of Family Medicine and lead for the PEER Knowledge Translation team at the University of Alberta.
MD CCFP
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Michael R. Kolber
Family physician, Professor in the Department of Family Medicine at the University of Alberta, and Director of Emprss (Electronic Medical Procedure Reporting Systems).
MD CCFP MSc
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Michelle Greiver
Family physician at North York General Hospital in Toronto, Associate Professor in the Department of Family and Community Medicine at the University of Toronto, and CPCSSN Network Director for UTOPIAN (University of Toronto Practice-Based Research Network).
MD CCFP FCFP MSc
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Scott R. Garrison
Family physician, Associate Professor in the Department of Family Medicine at the University of Alberta, and Director of the Pragmatic Trials Collaborative (Multi-Provincial Practice-Based Research Network).
MD CCFP PhD
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  • For correspondence: scott.garrison@ualberta.ca
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  • Figure 1.
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    Figure 1.

    Flowchart of cohort creation

    AF—atrial fibrillation, CPCSSN—Canadian Primary Care Sentinel Surveillance Network, DVT—deep vein thrombosis, INR—international normalized ratio, PE—pulmonary embolism.

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    Figure 2.

    Proportion of TTR for A) the 13 481 patients taking warfarin (with an INR target range of 2.0 to 3.5) and B) the 5556 patients taking warfarin with known AF, DVT, or PE (with an INR target range of 2.0 to 3.0): Both were determined over the 2008 to 2016 study period.

    AF—atrial fibrillation, DVT—deep vein thrombosis, INR—international normalized ratio, PE—pulmonary embolism, TTR—time in therapeutic range.

  • Figure 3.
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    Figure 3.

    Predictive value of baseline TTR: The top histograms are year 1 of warfarin use, with blue indicating good INR control, white intermediate INR control, and yellow poor INR control. The bottom histograms show the distribution of the same patients in year 2 with the same colour coding (eg, the second all-blue histograms show the TTR distribution in year 2 for all patients whose TTR was > 75% in year 1). N = 8054.

    AF—atrial fibrillation, DVT—deep vein thrombosis, INR—international normalized ratio, PE—pulmonary embolism, TTR—time in therapeutic range.

  • Figure 5.
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    Figure 5.

    Distribution of INR readings and all recorded INR values from October 2009 to October 2010 in patients with AF, DVT, or PE taking warfarin: Dark blue indicates INR values out of the low-risk range. Light blue is above the presumed 2.0 to 3.0 target for patients with these indications but within the low-risk range. N = 2184.

    AF—atrial fibrillation, DVT—deep vein thrombosis, INR—international normalized ratio, PE—pulmonary embolism.

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    Table 1.

    Patient characteristics

    PATIENT CHARACTERISTICSALL WARFARIN USERS (N = 13 481)THOSE WITH AF (N = 5010)THOSE WITH VTE (N = 730)
    Female sex, n (%)6285 (46.6)2221 (44.3)379 (51.9)
    Mean (SD) age, y71.9 (14.0)75.1 (11.3)63.1 (15.9)
    Mean (SD) BMI, kg/m230.1 (6.8)30.2 (6.5)31.8 (7.3)
    Mean (SD) GFR, mL/min64.7 (19.9)58.2 (16.7)56.3 (17.7)
    Comorbidities, n (%)
      • Hypertension8103 (60.1)3349 (66.9)370 (50.7)
      • Osteoarthritis4852 (36.0)2149 (42.9)288 (39.5)
      • Diabetes4144 (30.7)1670 (33.3)178 (24.4)
      • Depression3075 (22.8)1061 (21.2)233 (31.9)
      • COPD2747 (20.4)1146 (22.9)125 (17.1)
      • Dementia1770 (13.1)731 (14.6)62 (8.5)
    Warfarin-related condition, n (%)
      • AF5010 (37.2)5010 (100.0)184 (25.2)
      • DVT621 (4.6)160 (3.2)621 (85.1)
      • PE131 (1.0)33 (0.7)131 (18.0)
    Medications, n (%)
      • ≥ 4 medications (including warfarin)7120 (52.8)2807 (56.0)292 (40.0)
      • Cardiovascular drugs9973 (74.0)4179 (83.4)340 (46.6)
      • Lipid-modifying drugs5779 (42.9)2187 (43.7)179 (24.5)
      • Drugs for acid disorders4323 (32.1)1707 (34.1)202 (27.7)
      • Drugs for COPD or asthma3085 (22.9)1213 (24.2)134 (18.4)
      • Antidepressants2961 (22.0)1029 (20.5)186 (25.5)
      • Thyroid-related drugs1975 (14.7)799 (16.0)73 (10.0)
      • Antiepileptics1743 (12.9)660 (13.2)125 (17.1)
      • Anxiolytics1510 (11.2)510 (10.2)62 (8.5)
      • ASA967 (7.2)499 (10.0)39 (5.3)
      • Other antiplatelets457 (3.4)165 (3.3)10 (1.4)
      • Psycholeptics576 (4.3)196 (3.9)46 (6.3)
      • Anti-dementia drugs381 (2.8)132 (2.6)5 (0.7)
    • AF—atrial fibrillation, ASA—acetylsalicylic acid, BMI—body mass index, COPD—chronic obstructive pulmonary disease, DVT—deep vein thrombosis, GFR—glomerular filtration rate, PE—pulmonary embolism, VTE—venous thromboembolism.

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Canadian Family Physician: 65 (6)
Canadian Family Physician
Vol. 65, Issue 6
1 Jun 2019
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Quality of warfarin management in primary care
Sharon Liu, Alexander Singer, Finlay A. McAlister, William Peeler, Balraj S. Heran, Neil Drummond, Donna P. Manca, G. Michael Allan, Christina Korownyk, Michael R. Kolber, Michelle Greiver, Scott R. Garrison
Canadian Family Physician Jun 2019, 65 (6) 416-425;

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Quality of warfarin management in primary care
Sharon Liu, Alexander Singer, Finlay A. McAlister, William Peeler, Balraj S. Heran, Neil Drummond, Donna P. Manca, G. Michael Allan, Christina Korownyk, Michael R. Kolber, Michelle Greiver, Scott R. Garrison
Canadian Family Physician Jun 2019, 65 (6) 416-425;
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