The unrecognized psychosocial factors contributing to bleeding risk in warfarin therapy.

BACKGROUND AND PURPOSE Warfarin is an effective drug for the prevention of thromboembolism in the elderly. The major risk for patients taking warfarin is bleeding. We aimed to assess the impact of psychosocial factors, including mood, cognition, social isolation, and health literacy on warfarin instability among community-based elderly patients. METHODS A case-control study was conducted between March 2008 and June 2009 in a community-based setting. Cases were patients previously stabilized on warfarin who recorded an international normalized ratio≥6.0. Control subjects were patients whose international normalized ratio measurement was maintained within the therapeutic range. Patient interviews investigated potential predisposing factors to elevated International Normalized Ratio levels. RESULTS A total of 486 patients were interviewed: 157 cases and 329 control subjects, with an approximate mean age of 75 years. Atrial fibrillation was the most common primary indication. Adjusted multivariate logistic regression revealed impaired cognition (OR, 1.9; 95% CI, 1.0 to 3.6), depressed mood (OR, 2.2; 95% CI, 1.2 to 3.9), and inadequate health literacy (OR, 4.0;95% CI, 2.1 to 7.4) were associated with increased risk of an elevated International Normalized Ratio. CONCLUSIONS This study identified impaired cognition, depressed mood, and inadequate health literacy as risk factors for warfarin instability. These had a similar impact to well-recognized demographic, clinical, and medication-related factors and are prevalent among the elderly. These findings suggest that elderly patients prescribed warfarin should be reviewed regularly for psychosocial deficits.