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; Scott R. Garrison

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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.
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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.
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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 CHARACTERISTICS	ALL 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, y	71.9 (14.0)	75.1 (11.3)	63.1 (15.9)
Mean (SD) BMI, kg/m²	30.1 (6.8)	30.2 (6.5)	31.8 (7.3)
Mean (SD) GFR, mL/min	64.7 (19.9)	58.2 (16.7)	56.3 (17.7)
Comorbidities, n (%)
• Hypertension	8103 (60.1)	3349 (66.9)	370 (50.7)
• Osteoarthritis	4852 (36.0)	2149 (42.9)	288 (39.5)
• Diabetes	4144 (30.7)	1670 (33.3)	178 (24.4)
• Depression	3075 (22.8)	1061 (21.2)	233 (31.9)
• COPD	2747 (20.4)	1146 (22.9)	125 (17.1)
• Dementia	1770 (13.1)	731 (14.6)	62 (8.5)
Warfarin-related condition, n (%)
• AF	5010 (37.2)	5010 (100.0)	184 (25.2)
• DVT	621 (4.6)	160 (3.2)	621 (85.1)
• PE	131 (1.0)	33 (0.7)	131 (18.0)
Medications, n (%)
• ≥ 4 medications (including warfarin)	7120 (52.8)	2807 (56.0)	292 (40.0)
• Cardiovascular drugs	9973 (74.0)	4179 (83.4)	340 (46.6)
• Lipid-modifying drugs	5779 (42.9)	2187 (43.7)	179 (24.5)
• Drugs for acid disorders	4323 (32.1)	1707 (34.1)	202 (27.7)
• Drugs for COPD or asthma	3085 (22.9)	1213 (24.2)	134 (18.4)
• Antidepressants	2961 (22.0)	1029 (20.5)	186 (25.5)
• Thyroid-related drugs	1975 (14.7)	799 (16.0)	73 (10.0)
• Antiepileptics	1743 (12.9)	660 (13.2)	125 (17.1)
• Anxiolytics	1510 (11.2)	510 (10.2)	62 (8.5)
• ASA	967 (7.2)	499 (10.0)	39 (5.3)
• Other antiplatelets	457 (3.4)	165 (3.3)	10 (1.4)
• Psycholeptics	576 (4.3)	196 (3.9)	46 (6.3)
• Anti-dementia drugs	381 (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.