Fecal hemoglobin excretion in elderly patients with atrial fibrillation: Combined aspirin and low-dose warfarin vs conventional warfarin therapy

Background: Antithrombotic prophylaxis using combined aspirin and low- dose warfarin is under evaluation in several clinical trials. However, combination therapy may result in increased gastrointestinal blood loss and clinical bleeding vs conventional single-agent antithrombotic therapy. Methods: To assess differences in gastrointestinal blood loss, we measured quantitative fecal hemoglobin equivalents (HemoQuant, Mayo Medical Laboratory, Rochester, Minn) in 117 patients, mean age 71 years, 1 month after initiation of assigned therapy in the Stroke Prevention in Atrial Fibrillation III Study. Sixty-three of these patients who had characteristics for high risk of stroke were randomly assigned to conventional adjusted-dose warfarin therapy (international normalized ratio, 2.0 to 3.0) or low-dose combined therapy (warfarin [international normalized ratio, < 1.5] plus 325 mg/d of enteric-coated aspirin). The remaining 54 patients with low risk of stroke received 325 mg/d of enteric-coated aspirin. Results: Among the 63 patients at high risk of stroke, abnormal values (>2 mg of hemoglobin per gram of stool) were detected in 11% and values greater than 4 mg of hemoglobin per gram of stool were found in 8%. Mean (±SD) values were more for those randomly assigned to receive combined therapy (1.7±3.3 mg of hemoglobin per gram of stool vs adjusted-dose warfarin therapy, 1.0 ± 1.9 mg/g; P=.003). The 54 nonrandomized patients with low risk of stroke receiving aspirin alone had a mean (±SD) HemoQuant value of 0.8±0.7 mg of hemoglobin per gram of stool 1 month after entry in the study. Conclusions: Abnormal levels of fecal hemoglobin excretion were common in elderly patients with high risk of atrial fibrillation 1 month after randomization to prophylactic antithrombotic therapy. Combined warfarin and aspirin therapy was associated with greater fecal hemoglobin excretion than standard warfarin therapy, suggesting the potential for increased gastrointestinal hemorrhage.