Summary: Colonoscopy saved my life, but I was bleeding before I had one. The U.S. continues to use it as a screening test, without large studies. The Canadian response is that the harm possible from colonoscopy equals the possible colon cancer prevention if done widely on non-symptomatic patients.

Screening for Colorectal Cancer: An Updated Systematic Review [Internet].


Whitlock EP, Lin J, Liles E, Beil T, Fu R, O'Connor E, Thompson RN, Cardenas T.

Rockville (MD): Agency for Healthcare Research and Quality (US); 2008 Oct. Report No.: 08-05-05124-EF-1.

U.S. Preventive Services Task Force Evidence Syntheses, formerly Systematic Evidence Reviews.



We conducted a systematic review of five key questions to assist the U.S. Preventive Services Task Force (USPSTF) in updating its 2002 recommendation for colorectal cancer (CRC) screening in average-risk adults aged 50 years or older using home fecal occult blood testing (FOBT), flexible sigmoidoscopy (FS), FS and FOBT, colonoscopy, or double-contrast barium enema (DCBE). Key questions for this updated review primarily focused on evidence gaps from the previous review: 1) the accuracy (one-time test performance characteristics) and potential harms of newer CRC screening tests—fecal immunochemical tests (FIT), high-sensitivity FOBT, fecal DNA testing, and CT colonography (CTC)—as possible substitutes for currently recommended CRC screening modalities; 2) updating of evidence on the impact of CRC screening on mortality and to estimate the accuracy and harms of colonoscopy and FS in the community setting. A concurrent decision analysis done by others addressed screening program performance, and compared the life-years gained using different CRC screening tests, test intervals, and stopping ages.


We conducted five literature searches of MEDLINE and the Cochrane Library through January 2008. We identified 3948 abstracts from these searches and 488 articles identified from literature searches and outside sources, which we reviewed against specified inclusion-exclusion criteria. Articles were also excluded for quality reasons. Two reviewers' assents were required to exclude a study.


One investigator abstracted key elements of all included studies into standardized evidence tables. A second reviewer verified these data. Two investigators critically appraised and quality-rated all studies. Disagreements were resolved by consensus.


We reported quantitative synthesis for results of each key question, where possible, and qualitative synthesis otherwise. Impact of Screening on CRC Mortality. We found no new studies of CRC screening that report mortality outcomes; longer-term follow-up of four biennial FOBT screening trials indicates CRC mortality was reduced 13 to 21 percent after 8 to 13 years of screening in two trials, although another two trials did not show mortality benefit until after 15 to18 years of screening. The Cochrane Collaboration's pooled estimate of CRC mortality reduction in all four FOBT trials at last follow-up was 15 percent, using either random or fixed-effect models (RR 0.85, CI: 0.78,0.92). FITs, HemeSensa, fecal DNA. The largest body of evidence to evaluate screening test performance of newer fecal tests in average-risk screening populations is for fecal immunochemical tests (FITs), which cannot be analyzed as a class, but as individual assay types. Specifically, four individual FITs (Magstream/HemeSelect; FlexSure OBT/Hemoccult ICT; OC-Hemodia; Monohaem) have higher sensitivity for CRC (61 to 91 percent) than estimates for nonrehydrated Hemoccult II (25 to 38 percent) from another recent systematic review, with somewhat reduced specificity (91 to 97 percent). Sensitivity for advanced neoplasia or large adenomas is less commonly reported, but ranges between 20 and 67 percent in FITs, which is comparable or superior to the sensitivity for nonrehydrated Hemoccult II. Better detection appears to occur with 2 to 3 days of sample collection. For FITs, however, there is a mismatch between tests with clinical accuracy data and those with FDA approval and current US market availability. Of the four FITs discussed here, FlexSure OBT/Hemoccult ICT is the only FIT that is both FDA approved and on the US market at the time of this article. Fewer acceptable-quality studies evaluate Hemoccult Sensa, and although it appears to improve sensitivity for CRC (64 to 80 percent), it may also lower specificity (87 to 90 percent). Clinical accuracy data on fecal DNA tests is still too limited to support population screening, and there is a mismatch between available clinical studies and commercially available tests. Where test accuracy results do not indicate superior test sensitivity with comparable specificity, determining the trade-offs between sensitivity and specificity of newer tests for fecal CRC screening in a program of CRC screening requires modeling. CT Colonography. Published reports on CT colonography (CTC) screening suggest at least comparable sensitivity to colonoscopy for CRC and large adenomas (10 mm or larger). For smaller polyps (6 mm or larger), published data are inconsistent, with some studies suggesting reduced sensitivity or sensitivity, perhaps contingent upon the CT technology used and the individual reader. Published specificity estimates for CTC are consistently high (≥ 96 percent) for large polyps, but appear lower and more variable (80 to 94 percent) for smaller polyps (6 mm or larger). Test performance estimates will be more precise (more than doubling the number of average-risk patients studied with CTC screening) when currently unpublished data from the ACRIN study are made available. Based on currently published studies, as few as 1 in 8 to 1 in 13 of those screened with CTC would be referred for colonoscopy (if the referral threshold is CTC-detected lesions of 10 mm or greater), or, as many as 1 in 3 to 1 in 5 would be referred for colonoscopy (if the referral threshold is CTC-detected lesions of 6 mm or greater). Few procedure-related harms associated with CTC have been reported, although low-dose ionizing radiation is a potential harm. Additionally, extracolonic findings are relatively common (27 to 69 percent have any findings; 4 to 10 percent have findings of high clinical significance that require treatment or diagnostic evaluation; 5 to 27 percent have findings that would likely require investigation and/or further treatment); the net impact of all of these, in terms of added benefit (or harms), is uncertain. Accuracy and Harms of FS and Colonoscopy in Community Settings. In community settings, FS (with or without biopsy to determine colonoscopy referral) has an estimated sensitivity of 58 to 75 percent for CRC in the entire colon (based on small numbers) and an estimated sensitivity of 72 to 86 percent for advanced neoplasia. Variations in these estimates are likely due to differences in examiner skill and the patient's risks for proximal lesions in the unexamined colon. The performance of FS screening will become more clear after results of current randomized controlled trials (RCT) are reported. While colonoscopy remains the most accurate screening test for CRC at a single application, recent CTC studies have confirmed that colonoscopy misses polyps and may also miss CRC. Colonoscopy also presents a higher risk for harms than other tests. Serious harms from community endoscopies are about ten times more common with colonoscopy (3.1 per 1000 procedures) than with FS (3.4 per 10,000 procedures). The estimates for harms from FS, however, have much wider confidence intervals.


We reviewed the accuracy or harms of a CRC screening test in a single application for each question in this systematic review. The USPSTF commissioned a simultaneous decision analysis comparing different CRC screening programs that addressed repeated screening. Other topics beyond the scope of this review include barium enema for CRC screening, the adherence or acceptability of various CRC screening methods, methods to improve CRC screening rates, and cost-effectiveness.


Based on currently available evidence, refinements in current CRC screening recommendations to add some fecal tests appear warranted. Given potential harms and variation in test accuracy, emphasis on quality standards for implementation of recommended operator-dependent CRC screening tests also appears prudent. Re-evaluation may be appropriate once ongoing RCTs, particularly evaluating CTC, but also evaluating FS and fecal DNA, report their results. Screening for CRC has a rapidly evolving science base, such that guidance may be expected to change as additional research becomes available.

PMID: 20722162 [PubMed]

Ont Health Technol Assess Ser. 2009;9(10):1-40. Epub 2009 Sep 1.

Fecal occult blood test for colorectal cancer screening: an evidence-based analysis.

Health Quality Ontario.


The colorectal cancer (CRC) screening project was undertaken by the Medical Advisory Secretariat (MAS) in collaboration with the Cancer Care Ontario (CCO).In November 2007, the Ontario Health Technology Advisory Committee (OHTAC) MAS to conduct an evidence-based analysis of the available data with respect to colorectal cancer diagnosis and prevention. The general purpose of the project was to investigate the effectiveness, cost effectiveness, and safety of the various methods and techniques used for colorectal cancer screening in average risk people, 50 years of age and older.The options currently offered for colorectal cancer screening were reviewed and five technologies were selected for review:Computed tomographic (CT) colonographyMagnetic resonance (MR) colonographyWireless capsule endoscopy (PillCam Colon)Fecal occult blood test (FOBT)Flexible sigmoidoscopyIn this review, colonoscopy was considered as the "gold standard" technique by which the effectiveness of all other modalities could be evaluated. An economic analysis was also conducted to determine cost-effectiveness of different screening modalities.Evidence-based analyses have been prepared for each of these technologies, as well as summary document that includes an economic analysis, all of which are presented at the MAS Web site:


The objective of this evidence review is to examine the effectiveness and cost-effectiveness of fecal occult blood testing (FOBT), including guaiac FOBT (gFOBT) and immunochemical FOBT (iFOBT), for use in colorectal cancer (CRC) screening in asymptomatic, average-risk adults. Specifically: Is the use of gFOBT or iFOBT associated with a reduction in CRC and overall mortality?What are the sensitivity and specificity of gFOBT and iFOBT for the detection of 1) CRC and 2) large polyps (≥ 1 cm)? CLINICAL NEED: CRC is the most common cause of non-tobacco related cancer death in Canada. It has been estimated that in 2007, 7,800 people were diagnosed with CRC in Ontario and 3,250 died from the disease, making the province's incidence and mortality rate of CRC amongst the highest in the world. DESCRIPTION OF TECHNOLOGY/THERAPY: THERE ARE TWO GENERAL TYPES OF FOBT THAT ARE CATEGORIZED ACCORDING TO THE ANALYTE DETECTED: guaiac FOBT (gFOBT) and immunochemical FOBT (iFOBT). Blood in the stool is a nonspecific finding but may originate from CRC or larger (>1 cm) polyps (small adenomatous polyps do not tend to bleed). Bleeding from cancers and larger polyps may be intermittent and not always detectable in a single sample. The FOBT thus requires regular testing that consists of collecting specimens from consecutive bowel movements. A positive gFOBT or iFOBT involves a diagnostic workup with colonoscopy to examine the entire colon in order to rule out the presence of cancer or advanced neoplasia. METHODS OF EVIDENCE-BASED ANALYSIS: A literature search was conducted from January 2003 to June 2008 that included OVID MEDLINE, MEDLINE In-Process and Other Non-Indexed Citations, EMBASE, the Cumulative Index to Nursing & Allied Health Literature (CINAHL), The Cochrane Library, and the International Agency for Health Technology Assessment/Centre for Review and Dissemination.


Patients at average risk for CRCAll patients must be at least 50 years of ageBiennial FOBT as a screening modality and use of colonoscopy as the reference standardSystematic reviews and randomized controlled trials (RCTs)


CRC mortality, overall mortality, sensitivity, specificity, adverse effects


Studies involving fewer than 100 patientsStudies that do not report sufficient data for analysis COMPARISONS OF INTEREST: Evidence exists for these comparisons of interest: gFOBT compared with the reference "gold standard" colonoscopy (or double-contrast barium enema where colonoscopy is incomplete or contraindicated)iFOBT compared with the reference gold standard colonoscopy (or DCBE where colonoscopy is incomplete or contraindicated)gFOBT compared with iFOBTThe quality of the diagnostic studies was examined according to the 'GRADE Working Group criteria' for grading quality of evidence and strength of recommendations for diagnostic tests and strategies.


SINGLE-TEST STUDIES: There is limited direct/indirect evidence that iFOBT has sensitivity/specificity superior to that of unrehydrated gFOBT for CRC detection: sensitivity for gFOBT:13% and 25%pooled iFOBT sensitivity:81%There is evidence that iFOBT and gFOBT have lower sensitivities for adenoma detection than for CRC detection: sensitivity for rehydrated gFOBT22%pooled iFOBT sensitivity28% REPEATED-TEST STUDIES: No trials have examined CRC mortality outcomes after repeated testing of iFOBT. Two RCTs from the United Kingdom and Denmark showed significant reduction in CRC mortality using unrehydrated gFOBT biennially Relative risk reductions of 13% (UK trial) and 16% (Danish trial); absolute difference of 0.1% (UK trial) and 0.2% (Danish trial).No significant reduction in overall mortalityInterval cancers (CRC that develop in the intervals between routine screening) UNITED KINGDOM TRIAL: 236 CRCs detected by positive test, 236 interval CRCs after negative testDANISH TRIAL: 120 CRCs detected by positive test, 146 interval CRCs after negative testUnrehydrated gFOBT has low sensitivity for CRC detection (45% in the UK trial and 54% in the Danish trial). true positive rate50% (United Kingdom and Danish RCTs)false positive rate5%-10%true negative rate90%-95% (from observational studies as RCTs did not report specificity)false negative rate50%ES Table 1:Guaiac FOBT - GRADE Quality of Evidence for InterventionsOutcomeDesignQualityConsistencyDirectnessOverall QualityCRCMortalityRCTDanishN = 137,485United KingdomN = 152,850No seriouslimitationsYes (RR reduction in 2 trials13% and 16%; absolutedifference 0.1% and 0.2%respectively).Age rangeDanish and UnitedKingdom study 45-75yearsHighCRC indicates colorectal cancer; FOBT, fecal occult blood test; GRADE, Grading of Recommendations Assessment, Development and Evaluation; RCT, randomized controlled trial.*Unlikely to be an important uncertainty.ES Table 2:GRADE Quality of Evidence for Diagnostic Tests: Implications of Testing Focusing on AccuracyNew Test and Reference TestPutative BenefitDiagnostic AccuracyPatient Outcomes and Expected Impact on ManagementSensitivitySpecificityTrue PositiveTrue NegativeFalse PositiveFalse NegativePresumed Influence on Outcomes Important to PatientsiFOBT and ColonoscopySimple, non-invasiveLessLessBenefit from diagnosis and treatment after confirmatory colonoscopySmall risk of bowel perforation during colonoscopyBenefit of reassuranceAnxiety/worry leading up to confirmatory colonoscopySmall risk of bowel perforation during confirmatory colonoscopyDetriment from delayed diagnosisDirectness of Evidence (Test Results) for Outcomes Important to PatientsSome uncertainty (until after confirmatory colonoscopy)No UncertaintyUncertaintyUncertaintyFOBT indicates fecal occult blood test; GRADE, Grading of Recommendations Assessment, Development and Evaluation.Es Table 3:Immunochemical FOBT - GRADE Quality of Evidence for Diagnostic StudiesNo. ofStudiesDesignLimitationsIndirectnessInconsistencyImprecise dataQuality6Diagnostic cohort (single test)(reference standard for positive and negative iFOBT results was colonoscopy)No serious limitationsTP Some uncertaintyTN No uncertaintyFP UncertaintyFN UncertaintyTP rate = 69%TN rate = 94%FP rate = 6%FN rate = 30%(from direct comparison study)Diagnostic cohort iFOBT sensitivities: 50% to 90%High I(2)in pooled sensitivity and specificityWide range in confidence intervals in direct comparison studyLow*FN indicates false negative; FOBT, fecal occult blood test; FP, false positive; Development and Evaluation; TN, true negative; TP, true positive.*Uncertainty until after confirmatory colonoscopy†Stress/worry for patient until confirmatory colonoscopy‡Detrimental effects due to delayed diagnosis.§For these 3 reasons, downgrade quality from High to Moderate.║For these 3 reasons, downgrade quality from Moderate to Low. CONSIDERATIONS FOR THE ONTARIO HEALTH SYSTEM: Executive Summary Table 4 shows the potential system pressures and benefit/risk analysis for the use of FOBT and colonoscopy to screen for CRC in average-risk adults, ages 50 and over in Ontario. Es Table 4:Summary of Potential System Pressures for FOBT ScreeningCriterionColonoscopyFOBTPrimarily prevent or detect cancer?Prevent and detectDetectFrequency of screeningEvery 10 yearsMust repeat at regular intervalsEvery 2 yearsMust repeat at regular intervalsLevel of evidenceObservational studiesRCTsBenefitsUsed as gold standard in studiesINTERVENTION GRADE QUALITY: High (gFOBT)DIAGNOSTIC GRADE QUALITY: Low (iFOBT)No RCTs examining the effectiveness of repeated iFOBT on CRC mortality reduction were identifiedLimited direct/indirect evidence that iFOBT has superior sensitivity/specificity to unrehydrated gFOBT for detection of CRCRisks0.1% risk of serious bleeding and perforation requiring surgery0.3% risk of serious complications (stroke/bleeding requiring hospitalization/ myocardial infarction)High interval cancer rateThe small benefit in CRC mortality reduction (absolute difference 0.1% to 0.2%) also coincides with a 0.3% risk of serious complications.Preparation requirementsNo food 1 day prior to examOffice/hospital visitComplete bowel preparationSedationEliminate citrus fruit and juices and vitamin C from diet for 3 days prior to/during stool collection.Person applies 2 samples per bowel movement (each occurring on 3 different days) onto test areas of FOBT cards.Resources required for screening asymptomatic, average-risk adults ≥ 50 yearsIncreased demand for colonoscopies and colonoscopists or nurses who perform colonoscopies. (ABSTRACT TRUNCATED)

PMID: 23074514