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Am Fam Physician. 2006;74(11):1952-1954

Rectal bleeding is a relatively common symptom encountered in primary care. Although the risk of colorectal cancer is believed to be low, this rarely has been studied in patients presenting to primary care physicians. Four studies in European countries reported cancer rates of 2.4 to 7.0 percent. The British National Institute for Health and Clinical Excellence guidelines advise that patients older than 40 years with six weeks of rectal bleeding and loose stools should be tested for colorectal cancer. Du Toit and colleagues carried out a prospective study in a rural English practice of four doctors (with an average yearly patient list of 4,426) over 10 years to establish the risk of colorectal cancer in patients presenting with rectal bleeding.

Beginning in 1993, all patients older than 45 years who presented with rectal bleeding were tested and monitored for outcomes. The testing was done by sigmoidoscopy, barium enema, or colonoscopy. A computer search each year for all patients undergoing one of these tests was used to verify that all eligible patients in the practice had been included in the study.

During the study, 265 patients presented with new-onset rectal bleeding (see accompanying table). Colorectal cancer was diagnosed in 15 of these patients, and 13 had adenomas. A new episode of rectal bleeding in a patient 45 years or older had a positive predictive value for colorectal cancer of 5.7 percent (4.9 percent for adenoma). The authors calculate that one out of 10 patients with new rectal bleeding had neoplastic changes. Only two of the patients with bleeding and colorectal cancer also reported loose stools. During the study, an additional 23 patients were diagnosed with colorectal cancer, and 20 were diagnosed with adenoma but had no rectal bleeding.

Age group (years)Mean practice populationNumber (%) with new rectal bleeding in 10.25 yearsIncidence of rectal bleeding per 1,000 patients per yearNumber (%) with colorectal neoplasia and rectal bleedingNumber with colorectal cancer (with or without rectal bleeding)
45 to 5456151 (9.1)8.92 (3.9)03
55 to 6476275 (9.8)9.61 (1.3)3 (4.0)7
65 to 7462763 (9.4)9.86 (9.5)4 (6.4)14
75 or older93976 (8.1)7.96 (7.9)6 (7.9)14
Total2,889265 (9.2)8.815 (5.7)*13 (4.9)†38

The authors conclude that about one out of 10 patients who present to a family physician because of rectal bleeding has colorectal cancer or adenoma. Because factors such as age and change in bowel habit do not appear to help identify patients at increased risk of neoplasia, the authors believe that all patients 45 years and older should be tested for malignancy if they have rectal bleeding.

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