Warfarin Initiation, Atrial Fibrillation, and Kidney Function: Comparative Effectiveness and Safety of Warfarin in Older Adults With Newly Diagnosed Atrial Fibrillation.
BACKGROUND
The effectiveness and safety of warfarin use among patients with atrial fibrillation (AF) and reduced kidney function are uncertain.


STUDY DESIGN
Community-based retrospective cohort study (May 1, 2003, to March 31, 2012) using province-wide laboratory and administrative data in Alberta, Canada.


SETTING & PARTICIPANTS
14,892 adults 66 years or older with new AF and a measurement of kidney function. Long-term dialysis patients or kidney transplant recipients were excluded.


PREDICTOR
Propensity scores were used to construct a matched-pairs cohort of patients with AF who did and did not have a warfarin prescription within a 60-day period surrounding their AF diagnosis.


OUTCOMES
Within 1 year of initiating warfarin therapy (or the matched date for nonusers): (1) the composite of all-cause death, ischemic stroke, or transient ischemic attack (also assessed as separate end points) and (2) first hospitalization or emergency department visit for a major bleeding episode defined as an intracranial, upper or lower gastrointestinal, or other bleeding.


MEASUREMENTS
Baseline glomerular filtration rate (GFR) was estimated using the CKD-EPI creatinine equation. Patients were matched within estimated GFR (eGFR) categories: ≥90, 60 to 89, 45 to 59, 30 to 44, and <30mL/min/1.73m2. Information for baseline characteristics (sociodemographics, comorbid conditions, and prescription drug use) was obtained.


RESULTS
Across eGFR categories, warfarin therapy initiation was associated with lower risk for the composite outcome compared to nonuse (adjusted HRs [95% CI] for eGFR categories ≥ 90, 60-89, 45-59, 30-44, and <30mL/min/1.73m2: 0.59 [0.35-1.01], 0.61 [0.54-0.70], 0.55 [0.47-0.65], 0.54 [0.44-0.67], and 0.64 [0.47-0.87] mL/min/1.73m2, respectively). Compared to nonuse, warfarin therapy was not associated with higher risk for major bleeding except for those with eGFRs of 60 to 89mL/min/1.73m2 (HR, 1.36; 95% CI, 1.13-1.64).


LIMITATIONS
Selection bias.


CONCLUSIONS
Among older adults with AF, warfarin therapy initiation was associated with a significantly lower 1-year risk for the composite outcome across all strata of kidney function. The risk for major bleeding associated with warfarin use was increased only among those with eGFRs of 60 to 89mL/min/1.73m2.
['Jun|Min|M|', 'James|Matthew T|MT|', 'Ma|Zhihai|Z|', 'Zhang|Jianguo|J|', 'Tonelli|Marcello|M|', 'McAlister|Finlay A|FA|', 'Manns|Braden J|BJ|', 'Ravani|Pietro|P|', 'Quinn|Robert R|RR|', 'Wiebe|Natasha|N|', 'Perkovic|Vlado|V|', 'Wilton|Stephen B|SB|', 'Winkelmayer|Wolfgang C|WC|', 'Hemmelgarn|Brenda R|BR|', '|||']
D000368:Aged D000369:Aged, 80 and over D000416:Alberta D000419:Albuminuria D000925:Anticoagulants D001281:Atrial Fibrillation D002423:Cause of Death D015331:Cohort Studies D015897:Comorbidity D003404:Creatinine D005919:Glomerular Filtration Rate D006470:Hemorrhage D006801:Humans D002546:Ischemic Attack, Transient D009026:Mortality D057216:Propensity Score D051436:Renal Insufficiency, Chronic D012189:Retrospective Studies D020521:Stroke D014859:Warfarin
warfarin kidney function Atrial fibrillation (AF) death ischemic stroke stroke major bleeding antithrombotic therapy bleeding event cardiovascular disease chronic kidney disease (CKD) estimated glomerular filtration rate (eGFR) transient ischemic attack (TIA)