Summary of main findings
Rectal bleeding is common in the community and may be an early symptom of bowel cancer. This study shows that each year there are approximately 15 consultations for rectal bleeding in primary care per 1000 patients over the age of 34 years. The most useful factors in identifying higher risk groups were rectal bleeding in combination with a change in bowel habit to looser stools and/or an increased frequency of defaecation, bleeding without perianal symptoms and an age greater than 60 years.
The variation in the numbers of patients seen with rectal bleeding by GPs (from 8 to 37 per year) and in the timing of presentation in this study (from 16 to 49 per month) may be due to the difficulty in registering all patients with this symptom.6,8,9 As there were also differences between the practices there may be variations in patient consultation behaviour. The 15 per 1000 per year consultation rate in this study should be regarded as the minimum rate in the health district. Other studies have reported consultation rates of 4–16 per 1000 per year.1,8,9
The diagnosis of cancer in this study was based on flexible sigmoidoscopy, selective use of barium enema and colonoscopy, and an 18-month follow-up of all patients. As it has been shown that flexible sigmoidoscopy to 60 cm detects virtually all significant causes of bleeding in patients presenting with rectal bleeding to outpatients,19 it is likely that total colonic imaging in all patients would not have revealed any further cancers.
The prevalence of cancer in patients with rectal bleeding in general practice is important for the development of referral guidelines. As large numbers of people in the community have rectal bleeding,1–4 its predictive value for cancer in primary care will depend on the number of people deciding to seek medical advice and the accuracy with which this is recorded. Two studies in primary care6–8 have reported a 10% predictive value for cancer in patients referred and investigated in hospital, compared with 5–6% in all patients seen in primary care. These studies6–8 suggested that all patients with rectal bleeding over the age of 40 years seen in general practice should be referred to hospital for investigation. However, a Dutch9 and a Belgian study10 showing a 3.0% and 7.0% predictive value for cancer, respectively, suggested that selective referral policies were necessary.
Four previous studies8,11–13 have shown an increased risk of cancer when rectal bleeding was associated with a change in bowel habit. In this study all patients with cancer had an associated change in bowel habit, and in 90% (10/11) this was to an increased frequency of defaecation and/or to looser stools, the typical change in bowel habit in bowel cancer patients13,20 and giving a predictive value for cancer of 12%.
This study highlights the increased predictive value of rectal bleeding for cancer when perianal symptoms are absent. Other studies have shown that rectal bleeding with perianal symptoms in the absence of a change in bowel habit have a very low predictive value for bowel cancer, particularly when a rectal mass has been excluded.3,13
Abdominal pain has been emphasised in referral guidelines as an important alarm symptom.21 Although one study in primary care8 supports this view, this and three other studies11–13 have shown that it is of no extra diagnostic value.
Although age is an important diagnostic factor, in this study an age of greater than 60 years with a 5% predictive value for cancer was less useful for the identification of a higher risk group than when rectal bleeding was associated with a change in bowel habit, or it occurred without perianal symptoms, regardless of age, with predictive values for cancer of 9.2% and 11.1%, respectively.
Dark red bleeding and how it is noticed, are often thought to be of diagnostic value for cancer, although there is little evidence for this.7,8,11,15,22 In this study although dark rectal bleeding was associated with a higher predictive value for cancer, neither this nor the manifestations of rectal bleeding were of any significant diagnostic value.
In over a third of patients with cancer this was palpable, which once again emphasises the importance of a rectal examination in the management of patients with rectal bleeding in primary care.
Implications for clinical practice and future research
In addition to the recognition of the predictive value of combinations of symptoms and signs in identifying patients at higher risk of cancer, GPs will need to continue with the time-honoured way of selecting patients on the basis of ‘treat, watch-and-wait’ strategies. In the presence of these common symptoms of rectal bleeding — change in bowel habit, abdominal pain and perianal symptoms — a greater understanding is needed on the predictive value of these symptoms or combination of symptoms in identifying those patients at high risk of large bowel pathology. Only with the help of this information will it also be possible to accurately identify the much larger group of patients with transient symptoms from benign disease that will greatly benefit from not being referred.23
Rectal bleeding is a common problem in general practice with a low predictive value for cancer. The combination of rectal bleeding with a change in bowel habit to increased frequency of defecation with or without loose motions, and without perianal symptoms and an age over 60 years should be used to identify those patients at higher risk of cancer for more prompt referral to hospital. Patients at lower risk, and with a low level of anxiety regarding their symptoms can be treated for longer periods in primary care, so that those with transient bleeding from benign conditions can avoid hospital investigation.
