AIMS: To investigate the risk of stroke/thromboembolism (TE) and major bleeding associated with anaemia among patients with atrial fibrillation (AF). Also, to assess the effects of oral anticoagulation (OAC) and time in therapeutic range (TTR) with vitamin K antagonists according to level of haemoglobin (Hb).

METHODS AND RESULTS: Through administrative registry databases, we identified all Danish patients diagnosed with AF from 1997 to 2012. We included 18 734 AF patients with recent available data on Hb. Multiple Cox regression analyses were used to estimate hazard ratios and to compute standardized absolute 1-year risks of stroke/TE and major bleeding. Among included patients, 3796 (20%) had mild anaemia (Hb 6.83-7.45 mmol/L for women and Hb 6.83-8.03 mmol/L for men) and 2562 (14%) had moderate/severe anaemia (Hb <6.83 mmol/L). Moderate/severe anaemia was associated with increased risk of major bleeding and 9.1% lower median TTR compared with no anaemia. Use of OAC was associated with reduced risk of stroke/TE among patients without anaemia [standardized absolute 1-year difference -2.5%, 95% confidence interval (CI) -3.8 to -1.7%] or with mild anaemia (-2.3%, 95% CI -2.8 to -1.8%), but not with moderate/severe anaemia, (0.03%, -1.8 to +2.8%, interaction P = 0.01). Oral anticoagulation was associated with a 5.3% (95% CI 2.1-8.7%) increased standardized absolute risk of major bleeding among AF patients with moderate/severe anaemia.

CONCLUSION: Anaemia was common in patients with AF and associated with major bleeding and lower TTR. Oral anticoagulation was associated with more major bleeding, but no reduction in risk of stroke/TE among AF patients with moderate/severe anaemia.