***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: BACKGROUND Rectal bleeding is common , but it is still unclear which patients require investigation to exclude serious pathology , although it is known that colectoral cancer is very rare under the age of 40 years . Few studies have examined all patients presenting to their primary health physician rather than screening whole population s. AIM The aim of this study was to investigate the view that all patients over the age of 40 who present to their general practitioner with rectal bleeding should undergo investigation by colonoscopy to rule out serious pathology , regardless of symptomatology . METHOD A prospect i ve study was carried out of 99 consecutive patients over 40 years presenting with rectal bleeding to 17 general practice s in Newcastle upon Tyne . RESULTS Serious pathology was detected by colonoscopy in 44.4 % of patients . The diagnoses were : colorectal carcinoma , eight cases ( two Dukes ' grade A , two Dukes ' grade B , four Dukes ' grade C ) ; one or more polyps , 25 cases ( in 17 cases at least one polyp was 5 mm or greater in diameter ) ; inflammatory bowel disease , 11 cases . In the remaining 55 patients , bleeding was associated with diverticular disease ( 16 cases ) and haemorrhoids ( 28 cases ) . No cause was found in 11 patients . This high rate of pathology may be partly caused by selection of cases for referral by the general practitioner , despite efforts to minimize this . Three symptoms as elicited by the colonoscopist were found to be significantly associated with serious disease : blood mixed with stool ( P < 0.001 ) ; change in bowel habit ( P < 0.005 ) ; and the presence of abdominal pain ( P < 0.025 ) . However , symptoms elicited on primary presentation were less helpful and symptoms changed significantly between consultation with the general practitioner and colonoscopy . CONCLUSION All patients over the age of 40 years presenting with rectal bleeding should be referred for flexible sigmoidoscopy or colonoscopy . Symptoms are unhelpful in deciding who requires investigation Over a 3‐year period , all patients referred for barium enema examination  had a double‐contrast barium enema and flexible sigmoidoscopy performed on the same day . A total of 462 joint examinations were performed . Abnormalities were found in 193 patients by the use of barium enema , 164 patients by using sigmoidoscopy and 294 by the use of both methods of investigation .  Sigmoidoscopy was superior to barium enema in the detection of polyps and inflammatory bowel disease but barium enema was more sensitive for diverticular disease . The presenting symptoms had no predictive value in distinguishing carcinoma , polyps and diverticular disease . Diverticular disease did not reduce the sensitivity of barium enema examination to polyps in the sigmoid colon . Fibreoptic sigmoidoscopy immediately before barium enema was well tolerated by patients . The investigations were complementary in the diagnosis of colonic polyps , inflammatory bowel disease and diverticular disease The relationship between symptom duration and long-term survival following colorectal cancer is complex , and a number of factors may influence the length of time from onset of symptoms of cancer diagnosis . We prospect ively studied 777 consecutive colorectal cancer patients to determine the association between symptom duration and survival independent of other clinical and pathological features . We used survival curves , the logrank test and Cox 's proportional hazards model to assess possible changes in relative risk of death with increasing symptom duration , without making any a priori assumptions . We found that symptom duration shortened with advanced tumour stage ( P < 0.0006 ) and was also shorter for patients presenting with bowel obstruction ( P < 0.0001 ) . Univariate survival analysis showed that long-term survival increased consistently with symptom duration ( P < 0.001 ) . However , when the effect of tumour stage and bowel obstruction were accounted for in a multivariate analysis , no decrease in the relative risk of death was seen as symptom duration increased . The addition of other variables to the proportional hazards model such as age , sex or tumour site did not further influence the risk function form of symptom duration . Our results suggest that early diagnosis of colorectal cancer should remain our goal when assessing patients with suggestive gastrointestinal symptoms Although most cases of rectal bleeding are due to local conditions , this symptom is a major sign of colorectal cancer . Little research exists on whether to refer a patient with  rectal bleeding  for further evaluation.1 - 3 We therefore studied the diagnostic value of  rectal bleeding  in relation to a subsequent diagnosis of colorectal cancer . In Belgium , a network of sentinel practice s , covering 1 % of the population , registers epidemiological data .4 The methods used to estimate the denominator ( in patient years ) have been published.4 We analysed data on all patients with colorectal cancer diagnosed in 1993–4 to evaluate sensitivity ( retrospective study ) . We chose  rectal bleeding  as the reason for visiting a general practitioner before colorectal cancer was diagnosed as the main outcome measure . To obtain a positive predictive value ( prospect i ve part of study ) , we included all patients presenting with rectal bleeding in 1993 - 4 . Our reference st and ard was colorectal cancer diagnosed AIM To estimate the prevalence of colorectal cancer ( CRC ) in patients with long lasting colonic symptoms undergoing total colonoscopy ;  and to establish clinical features predicting its occurrence . METHODS This prospect i ve study was carried out in Imam Hospital , Tabriz University of medical sciences , Iran . Continuous patients with long lasting lower gastrointestinal tract symptoms who had the criteria of a colonoscopy were included . The endoscopist visualized the caecum documented by a photo and /or a specimen from terminal ileum . RESULTS Four hundred and eighty consecutive symptomatic patients [ mean age ( SD ) : 42.73 ( 16.21 ) ] were included . The prevalence of colorectal neoplasia  was 15.3 % ( 34 subjects ) and 37.7 % ( 181 subjects ) had a completely normal colon .  Adenomatous polyps were detected in 56 ( 11.7 % ) patients , in 12.3 % of men and 10.9 % of women . The mean age of the patients with a polyp was significantly higher than the others ( 49.53 + /- 14.16 vs 41.85 + /- 16.26 , P = 0.001 ) . Most of the adenomatous polyps were left sided and tubular ; only 22.5 % of polyps were more than 10 mm . Cancer was detected in 16 ( 3.6 % ) of our study population , which was mostly right sided ( 57.2 % ) . The mean age of patients with cancer  was significantly higher than the others ( 60.25 + /- 8.26 vs 42.13 + /- 16.08 , P < 0.005 ) and higher than patients with polyps [ 60.25 ( 8.26 ) vs 49.53 ( 1.91 ) ( P < 0.0005 ) ] . None of the symptoms ( diarrhea , abdominal pain , rectal bleeding , constipation , altering diarrhea and constipation , history of cancer , known irritable bowel disease , history of polyp and fissure or family history of cancer ) were predictors for cancer or polyps , but the age of the patient and unexplained anemia independently predicted cancer . CONCLUSION Less advanced patterns and smaller sizes of adenomas in Iran is compatible with other data from Asia and the Middle East , but in contrast to western countries . Prevalence of colonic neoplasia in our community seems to be lower than that in western population . Colonic symptoms are not predictors for polyps or cancer but unexplained anemia and elder age can predict CRC In a prospect i ve study involving 833 consecutive outpatient and open-access colonoscopies , attempts were made to characterize the benefit of colonoscopy in terms of both predicted and unpredicted findings and therapeutic procedures . The endoscopist therefore predicted the endoscopic findings before the endoscopy . The results were compared for the different indications for colonoscopy . The overall agreement between the predictions and the colonoscopic findings was 61 % . Clinical ly significant abnormalities were found in about half the examinations . The most frequent abnormal findings were benign polyps ( 24 % ) , inflammatory bowel disease ( 17 % ) , and malignancy ( 5 % ) . In about half the patients with a malignancy the indication for colonoscopy was rectal bleeding , and half of the malignancies were not predicted . The greatest benefit of colonoscopy  was found in patients referred because of overt rectal bleeding or occult faecal blood , and abnormal barium enema or endoscopy findings . The importance of complete colonoscopy in connection with operation for colorectal carcinoma is emphasized BACKGROUND AND OBJECTIVE A range of fixed-effect and r and om-effects meta-analytic methods are available to obtain summary estimates of measures of diagnostic test accuracy . The hierarchical summary receiver operating characteristic ( HSROC ) model proposed by Rutter and Gatsonis in 2001 represents a general framework for the meta- analysis of diagnostic test studies that allows different parameters to be defined as a fixed effect or r and om effects within the same model . The Bayesian method used for fitting the model is complex , however , and the model is not widely used . The objective of this report is to show how the model may be fitted using the SAS procedure NLMIXED and to compare the results to the fully Bayesian analysis using an example . METHODS The HSROC model , its assumptions , and its interpretation are described . The advantages of this model over the usual summary ROC ( SROC ) regression model are outlined . A complex example is used to compare the estimated SROC curves , expected operating points , and confidence intervals using the alternative approaches to fitting the model . RESULTS The empirical Bayes estimates obtained using NLMIXED agree closely with those obtained using the fully Bayesian analysis . CONCLUSION This alternative and more straightforward method for fitting the HSROC model makes the model more accessible to meta-analysts The aim of the study is to determine the diagnostic value of ( combinations of ) signs , symptoms and simple laboratory test results for colorectal cancer in patients with rectal bleeding presenting in general practice . Initial complaints and findings were compared with the final diagnoses based on clinical follow-up after at least 1 year . Patients studied were those presenting overt rectal bleeding to the general practitioner ( 83 GPs in the South of the Netherl and s ) . Outcome measures are sensitivity , specificity , predictive values , odds ratios and a prediction model derived from multiple logistic regression analysis . Age , change in bowel habit and blood mixed with or on stool show a statistically significant independent value in the discrimination between patients with a low and those with a high probability of colorectal cancer . Many other variables did not show predictive value . The prediction model has a sensitivitiy of 100 % and a specificity of 90 % . Although the number of patients with colorectal cancer is small ( n = 9 ) it was possible to identify three characteristics which can be helpful in the prediction of presence or absence of colorectal cancer in general practice . Application of the model presented might prevent 90 % of ' unnecessary ' invasive diagnostic procedures for patients with rectal bleeding who do not have colorectal cancer ( true negative ) . Testing the performance of the model in other general practice population s is recommended Colonoscopy is an integral part of the clinician armamentarium in the diagnosis of colorectal cancer and its precursor , the adenoma . Polypoid lesions when identified can be excised at colonoscopy and in turn reduce the risk of colorectal cancer . We prospect ively evaluated the yield of colorectal cancer and adenomatous polyps  by indication for colonoscopy  over a one-year period . A total of 375 colonoscopies were carried out . The more common indications of colonoscopy were rectal bleeding , abdominal pain , surveillance of colorectal cancer and altered bowel habit . The highest yield for cancer was for rectal bleeding with 12.5 % while surveillance of patients with a history of polyps yielded the highest percentage of new polyps . We conclude that rectal bleeding as an indication for colonoscopy yielded the highest number of cancers The aim of this study was to determine the prevalence of various kinds of bowel behavior and symptoms thought to be indicative of colorectal cancer in people r and omly selected from the community . A probability sample of 330 dwellings in the inner western suburbs of Sydney yielded 202 completed interviews with occupants aged 30 years and older . Eight percent reported annoying abdominal pain that had lasted for two weeks or more in the preceding six months , while 19 percent reported a feeling of incomplete evacuation at least once every two weeks .  Blood on the toilet paper  was reported by 14 percent and blood in the toilet bowl by 2 percent . Twenty-one percent said they always looked at their stool in the toilet bowl  and 34 percent always looked at the toilet paper after using it  , but 43 percent seldom or never looked at either their stool or the paper .  Of the 75 who said they looked at their stool about half the time or more , two ( 3.1 percent ) reported seeing blood during the preceding six months . Symptoms that may be associated with colorectal cancer are common in apparently well adults . Whilst this includes bleeding from the rectumin toto , it may not be true for blood seen specifically in the toilet bowl . Because this latter symptom has potential discriminating value , it may be worthwhile to promote public education encouraging people to inspect their stools regularly , and to visit their doctor if blood is seen OBJECTIVES To assess the clinical yield of colonoscoping in patients who present with rectal bleeding , persistent abdominal pain , or change in bowel habits in the absence of bleeding . DESIGN A prospect i ve study of  colonoscopy patients . SETTING Three colonoscopy practice s 
    Output:
    
Neither of these symptoms was associated with the presence of polyps .
There was no significant association of colorectal cancer or polyps with change in bowel habit , constipation , diarrhoea or abdominal pain .
Neither the clinical setting ( primary or specialist care ) nor study type was associated with accuracy .
Conclusions Current evidence suggests that the common practice of performing colonoscopies to identify cancers in people with bowel symptoms is warranted only for rectal bleeding and the general symptom of weight loss .