Background: Rectal bleeding is a recognised early symptom of colorectal cancer. This study aimed to assess the diagnostic accuracy of symptoms, signs and diagnostic tests in patients with rectal bleeding in relation to risk of colorectal cancer in primary care.
Methods: Diagnostic accuracy systematic review. Medline (1966 to May 2009), Embase (1988 to May 2009), British Nursing Index (1991 to May 2009) and PsychINFO (1970 to May 2009) were searched. We included cohort studies that assessed the diagnostic utility of rectal bleeding in combination with other symptoms, signs and diagnostic tests in primary care. An eight-point quality assessment tool was produced to assess the quality of included studies. Pooled positive likelihood ratios (PLRs), sensitivities and specificities were calculated.
Results: Eight studies incorporating 2323 patients were included. Average weighted prior probability of colorectal cancer was 7.0% (range: 3.3-15.4%, median: 8.1%). Age > or = 60 years (pooled PLR: 2.79, 95% confidence interval (CI) 2.00-3.90), weight loss (pooled PLR: 1.89, 95% CI: 1.03-3.07) and change in bowel habit (pooled PLR: 1.92, 95% CI: 0.54-3.57) raise the probability of colorectal cancer into the range of referral to secondary care but do not conclusively 'rule in' the diagnosis. Presence of severe anaemia has the highest diagnostic value (pooled PLR: 3.67, 95% CI: 1.30-10.35), specificity 0.95 (95% CI: 0.93-0.96), but still only generates a post-test probability of 21.6%.
Conclusions: In patients with rectal bleeding who present to their general practitioner, additional 'red flag' symptoms have modest diagnostic value. These findings have implications in relation to recommendations contained in clinical practice guidelines.