Rectal bleeding occurs in about 20 percent of the population annually and is commonly caused by benign problems; however, it can be indicative of colorectal cancer. Early detection of such neoplasms reduces cancer-related mortality. The risk of colorectal cancer before 40 years of age is low, and most recommendations for colon-cancer screening involve persons older than 40. Evaluation of rectal bleeding in older adults should include examination of the entire colon. In younger patients with rectal bleeding, the risk-benefit aspects of a full colon evaluation are less clear. Lewis and associates assessed the cost-effectiveness of a variety of evaluation strategies in young patients with asymptomatic rectal bleeding.

The authors developed a Markov analytic decision model of a 35-year-old patient presenting with asymptomatic rectal bleeding, defined as blood in the toilet bowl, on the tissue paper, or mixed with stool. This model analyzed nine potential evaluation strategies. The effectiveness of each diagnostic strategy was determined using probability estimates of rates of colonic neoplasms in persons 30 to 39 years of age; of the likelihood of persons with rectal bleeding having a colonic neoplasm; of rectal bleeding caused by benign anal disease; and of the rate at which adenomas progressed to invasive cancer. Direct medical costs for testing and care were obtained from Medicare reimbursement scales and National Institute of Cancer data.

The “no evaluation” strategy offered the lowest life expectancy, while colonoscopy or barium enema plus flexible sigmoidoscopy in all patients produced the greatest life expectancy. Strategies incorporating anoscopy offered greater life expectancy than no evaluation, but lower life expectancy than strategies that visualized all or part of the colon. Diagnostic strategies visualizing the entire colon offered greater life expectancy than strategies visualizing only part of the colon.

The incremental cost of flexible sigmoidoscopy was less than $5,300 per year of life gained; for flexible sigmoidoscopy plus barium enema, it was $23,918 per year of life gained; for colonoscopy, it was $50,193 per year of life gained. As anticipated, this cost increased for persons 25 years of age and decreased for persons 45 years of age because of variations in colon cancer incidence.

The authors conclude that, based on a cost-effectiveness analysis, rectal bleeding in adults older than the mid-30s should be evaluated with colonoscopy regardless of findings on anoscopy. In patients in their mid-20s or younger, flexible sigmoidoscopy alone or anoscopy followed by flexible sigmoidoscopy in patients without anal disease is probably more cost-effective than evaluation of the entire colon.