Predicting colorectal cancer risk in patients with rectal bleeding

Abstract

Background: Rectal bleeding is an important symptom of colorectal cancer but has low predictive value in primary care.

Aim: To determine which characteristics of rectal bleeding, along with other factors, are predictive of colorectal cancer.

Design of study: Observation study of patients with rectal bleeding referred to an open-access diagnostic clinic.

Setting: Primary care, southern England.

Method: Symptom data were collected, using a self-completed questionnaire. Logistic regression techniques were used to determine predictors of colorectal cancer.

Results: There were 604 patients in the study and 22 (3.6%, 95% confidence interval [CI] = 2.0% to 5.2%) were diagnosed with colorectal cancer. Significant predictors of colorectal cancer were found to be age (<50 years: odds ratio [OR] = 1; 50-69 years: OR = 5.1, 95% CI = 1.4 to 18.6; > or = 70 years: OR = 8.2, 95% CI = 2.1 to 31.8) and blood mixed with the stool (Likelihood ratio [LR] 1.5; adjusted OR = 3.8; 95% CI = 1.4 to 10.5). Presence of haemorrhoids associated with bright red bleeding not mixed with stool reduced the likelihood of cancer (OR = 0.4, 95% CI = 0.1 to 1.2) but did not eliminate it--a cancer was present in 2% of patients with these symptoms.

Conclusion: Patient-reported type of rectal bleeding as an isolated symptom has insufficient diagnostic value to be useful in general practice. By studying referred patients, we may even have overestimated its value. At best, it could be useful as a component of a composite symptom score to guide referral decisions.