Critical appraisal:Hundt S, Haug U, Brenner H 2009 2

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Risk of bias assessment: diagnostic accuracy study

Patient Selection
Prior tests and any referral filters
Condition that defined entry into study
The study includes participants undergoing screening colonoscopy—a procedure that the German health care system has offered since October 2002 to average-risk persons 55 years or older. All participants had a preliminary consultation with a gastroenterologist to receive detailed information and advice about screening colonoscopy. They were informed about and invited to participate in the study at that time
Setting
Was a diagnostic case-control design avoided?
Yes
Consecutive or random sample?
Yes
Did the study avoid inappropriate exclusions?
Yes
Reasons
111 were excluded because of visible rectal bleeding or preceding positive FOBT result

We excluded 13 patients because of inflammatory bowel disease
We excluded 117 patients because they had undergone colonoscopy in the past 5 years and thus would not be eligible for primary FOBT screening
We further excluded participants whose stool samples were collected after colonoscopy only (and thus violated the study protocol [n �=65]), those with inadequate bowel preparation before colonoscopy (n =79), and those with incomplete colonoscopy (that is, the cecum was not reached, [n �=22])
We excluded patients who received a histologically confirmed diagnosis of CRC
We excluded 10 participants with nondefined polyps (no histologic reports were available)
We excluded participants with pseudopolyps (n �=38)

If comparing more than one index test was the design fully paired or paired randomly?
Not applicable
If a paired randomised design was used, was allocation to groups concealed and was the generation of allocation sequence adequate?
Not applicable
What is the risk that the selection of participants introduced bias?
Low
Comments
Index test 1
Describe index test and how it was conducted and interpreted
6 different qualitative immunochemical FOBTs were done with stool samples collected before bowel preparation for colonoscopy. Performance characteristics (sensitivity, specificity, predictive values, and likelihood ratios) of tests were measured by comparing test results with findings on colonoscopy. Technicians who read the tests were blinded to colonoscopy results, and colonoscopists were blinded to FOBT results.
Were the index test results interpreted without knowledge of the results of the reference standard?
Yes
If a threshold was used, was it pre-specified?
Yes
If two tests are being compared, have they been assessed independently / blind to each other?
Not applicable
What is the risk that the conduct or interpretation of the index test introduced bias?
Low
Comments
We did all analyses according to the manufacturers’ instructions and under standardized conditions
Index test 2
Describe index test and how it was conducted and interpreted, if applicable
Were the index test results interpreted without knowledge of the results of the reference standard?
Not applicable
If a threshold was used, was it pre-specified?
Not applicable
What is the risk that the conduct or interpretation of the index test introduced bias?
Not applicable
Comments
6 different FOBTS are compared = 6 index tests.
Reference Standard
Describe the reference standard and how it was conducted and interpreted
The study includes participants undergoing screening colonoscopy—a procedure that the German health care system has offered since October 2002. For screening colonoscopy, patients are referred to the gastroenterologist only when the decision to have colonoscopy is made. Physicians who did colonoscopy and histologic examination were blinded to FOBT results.
Is the reference standard likely to correctly classify the target condition?
Yes
Were the reference standard results interpreted without knowedge of the results of the index test/s?
Yes
Was the reference test standard independent of the index test?
(i.e. the index test did not form part of the reference standard)
Yes
What is the risk that the reference standard, its conduct or interpretation introduced bias?
Low
Comments
Flow and timing
Describe any patients who did not receive the index test(s) and/or reference standard or who were excluded from the 2x2 table
Describe the time interval and any interventions between index test(s) and reference standard
Participants undergoing screening colonoscopy typically present at the gastroenterology practice for preliminary consultation about 1 week before colonoscopy
If a predictive test (the reference standard is a later event that the test aims to predict) were any subsequent interventions between test and later event blind to test result?
Not applicable
Was there an appropriate interval between index test(s) and reference standard?
Yes
Did either all participants or a random sample of participants receive a reference standard test?
Yes
Did all patients receive the same reference standard irrespective of index test result?
Yes
Were all test results including unclear results reported?
No
Were all patients included in the analysis?
Yes
What is the risk that the patient flow introduced bias?
Low
Comments
Overall risk of bias
Low risk of bias Additional comments: Please replace this text and include any additional comments in regards to your risk of bias rating


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Article
Hundt S, Haug U, Brenner H. Comparative evaluation of immunochemical fecal occult blood tests for colorectal adenoma detection. Ann Intern Med 2009 Feb 3;150(3):162-9 Available from: http://www.ncbi.nlm.nih.gov/pubmed/19189905.
Assigned to
User:Ben.lee-bates
Topic area
Guidelines:Colorectal cancer
Clinical question
Form
Form:Quality appraisal quadas


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