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Single Office-Based Fecal Occult Blood TestingMay Be Inadequate for Colorectal Screening CME News Author: Laurie Barclay, MDCME Author: Charles Vega, MD, FAAFP

Disclosures

To earn CME credit, read the news brief along with the CME information that follows and answer the test questions.

Release Date: January 18, 2005; Valid for credit through January 18, 2006

This activity has expired.CME in this activity indicates that it was developed according to ACCME guidelines and was certified for credit by anaccredited CME provider. Medscape cannot attest to the timeliness of expired CME activities.

Jan. 18, 2005 — Single office-based fecal occult blood testing (FOBT) is not adequate for colorectalscreening, but a large survey of physicians showed that it is often used, according to the results oftwo studies published in the Jan. 18 issue of the Annals of Internal Medicine . The editorialistemphasizes the need to change this practice.

"Many expert panels recommend colorectal cancer screening for average-risk asymptomaticindividuals older than 50 years of age," write Judith F. Collins, MD, from the Department of

Veterans Affairs Medical Centers in Portland, Oregon, and colleagues from the Veterans AffairsCooperative Study #380 Group. "Recent studies have found that 24% to 64% of primary careproviders use only the digital fecal occult blood test (FOBT) as their primary screening test. Theeffectiveness of a single digital FOBT is unknown."

This prospective cohort study conducted at 13 Veterans Affairs Medical Centers compared thesensitivity and specificity of digital FOBT and the recommended six-sample, at-home FOBT foradvanced neoplasia in asymptomatic individuals.

Of 3,121 asymptomatic patients aged 50 to 75 years, 2,665 patients had six-sample, at-homeFOBT and digital FOBT followed by complete colonoscopy. Average age was 63.1 years, and96.8% were men. For each test, the investigators calculated predictive values and likelihood ratiosfor advanced neoplasia, defined as tubular adenomas 10 mm or greater, adenomas with villoushistology or high-grade dysplasia, or invasive cancer.

Based on 1,656 patients with no neoplasia, specificity was 93.9% for the six-sample FOBT and97.5% for the single digital FOBT. For detection of advanced neoplasia, sensitivities were 23.9% forthe six-sample FOBT and 4.9% for the digital FOBT. The likelihood ratio for advanced neoplasiawas 1.68 (95% confidence interval [CI], 0.96-2.94) for positive results on digital FOBT and 0.98(95% CI, 0.95-1.01) for negative results.

Study limitations include predominantly male sample; rehydration used to develop six-sample, at-home FOBTs, which may have increased the sensitivity and decreased the specificity of this test;and reliance on the assumption that the endoscopists identified all significant neoplasia.

"Single digital FOBT is a poor screening method for colorectal neoplasia and cannot berecommended as the only test," the authors write. "When digital FOBT is performed as part of aprimary care physical examination, negative results do not decrease the odds of advanced

This activity hasexpired. The accredited providercan no longer issuecertificates for thisactivity. Medscape cannot

attest to the timeliness ofexpired CME activities.

CME Information

Medscape is accredited bythe Accreditation Council forContinuing MedicalEducation (ACCME) toprovide continuing medicaleducation for physicians.

Medscape designates thiseducational activity for 0.25category 1 credit(s) towardthe AMA Physician'sRecognition Award. Eachphysician should claim onlythose credits that reflect thetime he/she actually spent inthe activity.

of 4Single Office-Based FOBT May Be Inadequate for Colorectal...

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neoplasia. Persons with these results should be offered at-home six-sample FOBT or another typeof screening test."

The Cooperative Studies Program, Department of Veterans Affairs, supported this study. Theauthors report no conflicts of interests.

The accompanying report describes results from the Survey of Colorectal Cancer ScreeningPractices in Health Care Organizations and the 2000 National Health Interview Survey, which arecross-sectional national surveys of primary care physicians and the public.

"Screening with the FOBT has been shown to reduce colorectal cancer incidence and mortality inrandomized, controlled trials," write Marlon R. Nadel, PhD, from the Centers for Disease Controland Prevention and the American Cancer Society in Atlanta, Georgia, and colleagues. "Althoughthe test is simple, implementation requires adherence to specific techniques of testing and follow-upof abnormal results."

The surveys collected self-reported data on details of FOBT implementation and follow-up ofpositive results from 1,147 primary care physicians who ordered or performed FOBT, and from11,365 adults aged 50 years or older who responded to questions about FOBT use.

Despite screening guidelines recommending home FOBT, 32.5% of physicians (95% CI, 29.8%-35.3%) used only the less accurate method of single-sample in-office FOBT. An additional 41.2%(95% CI, 38.3%-44.0%) used both types of test.

Follow-up of positive test results often failed to adhere to established guidelines. Only 29.7% ofphysicians (95% CI, 27.1%-32.4%) recommended repeating FOBT, and sigmoidoscopy, rather thantotal colon examination, was often recommended to work up abnormal findings.

Of adults who reported having FOBT, nearly one third reported having only an in-office test. Ofthose who reported abnormal FOBT results, nearly one third reported no follow-up diagnosticprocedures.

Study limitations include reliance on self-reports, and possible underestimation of the prevalence ofin-office testing and inadequate follow-up using data from the National Health Interview Survey.

"Mortality reductions demonstrated with FOBT in clinical trials may not be realized in communitypractice because of the common use of in-office tests and inappropriate follow-up of positiveresults," the authors write. "Education of providers and system-level interventions are needed to

improve the quality of screening implementation."

The National Cancer Institute and the Centers for Disease Control and Prevention supported thisstudy. One of the authors reports a consultancy with EXACT Sciences Corp until 2002.

In an accompanying editorial, Harold C. Sox, MD, notes that using the home-based method resultsin fewer colonoscopies on patients who do not have advanced colonic neoplasia. This approachreduces costs and unnecessary adverse effects, while improving access to colonoscopy.

"These two studies discredit the office-based single-sample screening test for occult blood whilesimultaneously showing that it is common practice," Dr. Sox writes. "Taken together, they send astrong message to primary care physicians to reexamine their colorectal cancer screeningpractices. Perhaps we need to put the guaiac cards in a locked drawer labeled 'use only in case ofemergency.'"

Ann Intern Med. 2005;142:81-94, 146-148

Learning Objectives for This Educational Activity

Upon completion of this activity, participants will be able to:

Describe common errors in screening patients for colon cancer in the U.S. Compare single FOBT following digital rectal examination (DRE) vs a six-sample, at-home

FOBT in detecting colon neoplasia.

Clinical Context



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Colon cancer remains a significant risk of mortality for older adults, and screening for cancer withFOBT has been demonstrated to reduce the risk of mortality. However, an article by Nadel andcolleagues, which accompanies the current article in Annals of Internal Medicine , demonstrates thatthe practice of FOBT and follow-up for positive testing is frequently not performed correctly in theU.S. In a survey of physicians, 32.5% reported performing only in-office FOBT testing followingDRE as their method of screening for colon cancer, instead of recommended at-home tests ofmultiple stool samples. Moreover, follow-up of positive FOBT was disappointing among olderpatients. Of patients, 31.6% reported no follow-up for an abnormal result, while 6.3% reportedreceiving sigmoidoscopy alone.

In another study in this week's Annals of Internal Medicine , Collins and colleagues report on thesensitivity and specificity of single FOBT compared with six-sample, at-home FOBT in the detectionof colon neoplasia. Their results are summarized in the "Study Highlights."

Study Highlights

Participants were between the ages of 50 to 75 years and were drawn from 13 VeteransAffairs primary care clinics. Patients were excluded if they had symptoms of lowergastrointestinal tract disease or a history of such disease. No participant had any structuralexamination for colon cancer in the previous 10 years.

Subjects received both a single FOBT following DRE as well as materials and instructionsfor collecting 3 stool samples from home for FOBT testing. The home samples were placedon 2-window cards and rehydrated for a total of 6 tests per patient with this method.

All participants also underwent colonoscopy with biopsy of all visible polypoid lesions.

Physicians performing the colonoscopy were mostly blinded to FOBT results. The main study outcomes were the sensitivity and specificity of both types of FOBT in

predicting neoplasia of the colon, defined as tubular adenoma at least 10 mm in diameter,villous adenoma, high-grade dysplasia, or cancer.

2,665 subjects had both types of FOBT as well as colonoscopy. The mean age was 63.1years, and 96.8% of subjects were men.

45.7% of screened subjects had no polypoid lesions on colonoscopy, and 16.4% werediagnosed as having only hyperplastic or nonadenomatous polyps. The specificity of singleFOBT was 97.5% in these subjects compared with a specificity of 93.9% for 6-sampleFOBT.

27.2% of participants harbored tubular adenomas of less than 10 mm in diameter. 4% of thisgroup had positive single FOBT, while 6.3% had a positive 6-sample FOBT.

In subjects with advanced neoplasia, the rates of positive single FOBT and 6-sample FOBTwere 4.9% and 23.9%, respectively. Single FOBT was positive in only 6.4% of participantswith high-grade dysplasia and 9.5% of subjects with cancer. The same respective values for6-sample FOBT were 29.8% and 42.9%.

The overall sensitivity and specificity for single FOBT in the detection of colon neoplasiawere 4.9% and 97.1%, respectively. The same values for the 6-sample FOBT were 23.9%and 93.8%, respectively.

The positive predictive values for advanced neoplasia were 31.6% and 16.7% for 6-sampleand single FOBT, respectively. Their negative predictive values were 91.2% and 89.5%,respectively.

While a positive single FOBT result was associated with an increased likelihood ratio ofadvanced neoplasia (likelihood ratio, 1.68), this result did not reach statistical significance. Anegative single FOBT result did not have any significant predictive value whatsoever(likelihood ratio, 0.98).

Adding 6-sample FOBT to single FOBT significantly increased the sensitivity of single FOBT,while the converse was not true.

Among patients with no index adenoma in the rectum or sigmoid colon, the sensitivity of the6-sample FOBT was 17.2% compared with a value of 4.9% for single FOBT.

Pearls for Practice

U.S. physicians frequently use inappropriate means, including single FOBT andsigmoidoscopy following abnormal FOBT, in screening for colon cancer.

Single FOBT vs six-sample, at home FOBT is not of any practical use in screening for coloncancer in men.

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