Copenhagen, Denmark—When patients treated with blood thinners for atrial fibrillation complain of lower gastrointestinal track bleeding, pharmacists and other healthcare professionals shouldn’t just assume that is a side effect of oral anticoagulant drugs.

That’s according to a study published in the European Heart Journal, which also urges that those patients be screened for bowel cancer.

A study of nearly 125,500 Danish patients with atrial fibrillation (AFib) concludes that those who experienced bleeding were between 11 and 24 times more likely to be diagnosed with bowel cancer, compared with patients who did not have gastrointestinal (GI) bleeding.

“We found that between four and eight per cent of atrial fibrillation patients who experienced bleeding from their lower gastrointestinal tract were diagnosed with bowel cancer. Less than one per cent of patients were diagnosed with bowel cancer if they did not have bleeding,” explained lead author Peter Vibe Rasmussen, MD, from the University of Copenhagen. “These high absolute risks of bowel cancer associated with bleeding provide a strong argument that if blood is detected in the stools of patients being treated with oral anticoagulants, this is something doctors should worry about.”

Dr. Rasmussen added, “Our findings underline the important point that patients with gastrointestinal bleeding should always be offered meticulous clinical examination, irrespective of whether or not they are taking anticoagulants. It should not be dismissed as a mere consequence of anticoagulant treatment.”

The study team identified 125,418 Danish atrial fibrillation patients initiating oral anticoagulant therapy from Danish administrative registers. Over as many as 3 years of follow-up, researchers were able to identify 2,576 patients with lower GI bleeding. Of those, 140 patients were subsequently diagnosed with colorectal cancer within the first year of lower-GI bleeding.

The study notes that high risks of colorectal cancer after lower-GI bleeding occurred in all age groups. The absolute 1-year risk ranged from 3.7% [95% CI, 2.2-6.2] in the group younger than age 65 years and to 8.1% (95% CI, 6.1-10.6) in those aged 76 to 80 years.

“When comparing patients with and without lower GI-bleeding, we found increased risk ratios of colorectal cancer across all age groups with a risk ratio of 24.2 (95% CI, 14.5-40.4) and 12.3 (95% CI, 7.9-19.0) for the youngest and oldest age group of ≤65 and >85 years, respectively,” the authors write.
“Lower GI-bleeding should not be dismissed as a benign consequence of OAC therapy but always examined for a potential underlying malignant cause,” the researchers emphasize. “Our study is also a reminder that educating and informing our patients is of utmost importance,” Dr. Rasmussen added. “When patients start taking anticoagulants, we should tell them that if they see blood in their stools they should always consult their doctor. Timely examination could potentially provide early detection of bowel cancer.”

Patients with atrial fibrillation are often prescribed oral blood-thinning drugs, such as warfarin, dabigatran, rivaroxaban, and apixaban, to prevent the formation of clots that can lead to stroke. Bleeding from the GI tract can be a side effect and is estimated to occur in about 1% to 2% of AFib patients each year, according to the report.

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