PROGRESS
`
`ARTICLE
`
`GASTROENTEROLOGY
`
`1985;88:820-37
`
`Occult Blood Screening for Colorectal
`Carcinoma: A Critical Review
`
`JEROME B. SIMON
`Department
`of Medicine, Division
`Canada
`
`Review Contents
`
`of Gastroenterology,
`
`Queen’s University,
`
`Kingston, Ontario,
`
`Blood Loss
`
`the Reaction
`
`for Bowel Cancer
`Screening
`Relevant Screening Concepts
`Biases in Screening
`Occult Blood Detection-History
`Chemical Tests
`Nature of the Reaction
`Commercial Tests
`Other Tests
`“Normal” Gastrointestinal
`Specific Test Sensitivities
`Technical Factors Influencing
`Dietary Peroxidases
`Dietary Residue
`Slide Storage and Rehydration
`Drugs
`in Known Colorectal Tumors
`Occult Bleeding
`Reasons for Falsely Negative Tests
`Clinical Findings
`Uncontrolled
`Screening Studies
`Controlled Screening Studies
`University
`of Minnesota Program
`Sloan-Kettering
`Program
`Compliance
`costs
`Direct Costs
`Indirect Costs
`“Hidden” Costs
`Conclusions
`
`on occult blood
`the literature
`reviews
`The author
`for colorectal
`carcinoma.
`The guaiac-
`surveillance
`based Hemoccult
`(SmithKline Diagnostics,
`Sunny-
`vale, Calif.) test is the most reliable and widely used.
`However,
`testing is complicated
`by several
`technical
`issues
`that can affect clinical
`results,
`and even
`successful
`screening programs will miss a high pro-
`portion of tumors. Public compliance
`is often poor,
`and a number of indirect and “hidden”
`costs make
`surveillance
`programs much more expensive
`than is
`usually
`claimed. Almost
`all published
`screening
`trials are uncontrolled.
`They generally detect about
`for every 10,000 peo-
`3-20
`coJorectaJ malignancies
`ple enrolled, but only about 5%-10°h
`of occult blood
`reactions
`are due
`to cancer. Though
`screen-detected
`tumors
`tend
`to be at a relatively
`early stage,
`this
`does not imply any benefit of surveillance
`because
`of lead
`time and
`length biases
`inherent
`in
`the
`screening process. Only controlled
`trials can answer
`the central question of whether screening decreases
`mortality
`from bowel cancer. Two such
`trials are
`underway,
`but mortality
`data are not yet available
`from either.
`
`is both common and fatal. Indeed,
`Colorectal cancer
`in men it is exceeded only by cancer of the lung, and
`in women only by cancer of the breast, as a cause of
`tumor mortality
`in North America
`(1). Though many
`patients do survive
`this malignancy,
`the overall 5-yr
`survival rates are only 40%-45%
`(2,3). Moreover
`this
`figure has changed
`little for at least two decades
`(2).
`Thus earlier detection
`(4,5), rather
`than better
`treat-
`ment, probably offers the best hope for improving
`the
`outcome of this important
`disease.
`in the
`During
`the past 15 yr interest has grown
`concept of screening apparently healthy populations
`for bowel cancer by means of fecal occult blood
`detection. A massive
`literature
`on this subject has
`accumulated, much of it confusing. The purpose of
`
`by
`
`the Bureau
`
`Received March 6, 1984. Accepted
`11, 1984.
`September
`Address requests for reprints to: Dr. Jerome B. Simon, Queen’s
`University,
`Division
`of Gastroenterology,
`78 Barrie Street, Kings-
`ton, Ontario K7L 3J7, Canada.
`This work was
`supported
`Health
`and Welfare Canada.
`for her expert
`The author
`is grateful
`to Mrs. Ruth Pattenden
`searches
`of
`the
`assistance, Mrs. Vivian Ludwin
`for computer
`literature,
`and Mrs. Linda Miller
`for tireless
`secretarial
`help. Dr.
`S. J. Winawer
`kindly
`forwarded
`two manuscripts
`before
`their
`publication,
`and Dr. D. R. Brodie kindly
`provided
`an otherwise
`unobtainable
`copy of the proceedings
`of the 1978 National
`Insti-
`tutes of Health Consensus
`Conference.
`0 1985 by the American
`Gastroenterological
`0016.5085/85/$3.30
`
`of Medical Devices,
`
`Association
`
`Geneoscopy Exhibit 1033, Page 1
`
`

`

`

`

`822 SIMON
`
`GASTROENTEROLOGY Vol. 88. No. 3
`
`if no
`
`can result even
`apparent benefit of screening
`true benefit exists (8,12-14).
`is
`a population
`Length bias
`is maximal when
`initially screened; because most tumors are found at
`this initial testing,
`the bias diminishes during subse-
`quent surveillance
`of the same population
`(8).
`Patient
`selection
`bias (8,12,13). Screened
`populations may not accurately
`represent
`patients
`who develop
`a disease
`in general. For example,
`subjects
`in the Sloan-Kettering
`occult blood
`trial
`generally
`are middle
`class, highly motivated,
`and
`well educated
`(19). Perhaps
`the epidemiology
`and
`natural history of bowel cancer
`in such a group
`differs from that of a lower socioeconomic
`popula-
`tion which does not volunteer
`for screening. The
`impact of selection
`bias on screening
`programs
`is
`difficult
`to estimate, but any apparent benefit could
`at least partly be related
`to
`the
`type of patient
`selected.
`pro-
`screening
`of a colorectal
`The effectiveness
`that
`gram must ultimately
`rest on demonstration
`screening
`reduces mortality
`from bowel cancer. This
`in turn requires statistically valid comparison with a
`comparable
`group of the population which
`is not
`screened. As
`touched
`upon by various
`authors
`(ll,l4),
`especially
`Prorok
`(15), randomized,
`con-
`trolled clinical
`trials are best able to minimize
`the
`biases discussed
`above. Various other quasi-experi-
`mental methods
`of evaluating
`screening
`programs
`have been attempted, but these are difficult
`to inter-
`among the vast literature on
`pret (11). Unfortunately,
`occult blood screening, only two ongoing studies are
`potentially
`able to determine
`the impact on mortal-
`ity. These are detailed
`later.
`
`Occult Blood Detection-History
`is gen-
`The concept of occult blood detection
`to Van Deen, who in 1864 used gum
`erally credited
`guaiac as an indicator
`reagent; his
`test was
`later
`modified by many others
`(discussed
`in References
`20 and 21), and even today guaiac remains
`the most
`widely used
`indicator
`for occult bleeding.
`In the
`early 1900s Adler and Adler introduced benzidine as
`an alternative marker, and a host of technical varia-
`tions
`followed
`(discussed
`in References
`20-23).
`Over the years numerous other chemicals have been
`used to detect fecal blood, and new ones continue
`to
`be described
`to this day (20-29). Of all of these, only
`guaiac,
`benzidine,
`and orthotolidine
`have
`ever
`achieved
`any measure
`of acceptance. Moreover,
`since
`the late 1960s the latter
`two have fallen
`into
`disfavor-partly
`due to concern about their potential
`they are
`(30-32), but mainly because
`carcinogenicity
`too sensitive
`for clinical validity
`(see below).
`Boas
`in 1901 apparently
`first emphasized
`
`the
`
`of bowel
`for the detection
`value of occult blood
`malignancy (20), but for two-thirds of a century
`little
`attention was given
`to
`the concept
`of screening
`apparently
`healthy populations. Credit for stimulat-
`ing interest
`in this goes to Greegor, an Ohio internist.
`In the mid-1960s Greegor had guaiac-impregnated
`slides designed
`for his patients
`to use at home and
`mail
`to his office, and
`in 1967 he reported
`the
`detection
`of several asymptomatic
`tumors by this
`means (33). Subsequent
`studies confirmed
`the abili-
`ty of this slide
`test, known as Hemoccult
`(Smith
`Kline Diagnostics, Sunnyvale, Calif.) to uncover sub-
`clinical bowel cancer. As a result,
`throughout
`the
`1970s
`the
`literature
`on
`its use mushroomed
`and
`many screening
`studies were undertaken. Unfortu-
`nately
`these were too often ill designed and superfi-
`cial, and only gradually has a more critical approach
`to screening
`developed. This process continues
`to
`evolve.
`
`Chemical Tests
`Nature of the Reaction
`
`(20,23)
`
`tests for occult blood depend upon
`Chemical
`the oxidation of a phenolic
`compound
`to a quinone
`structure, which
`in turn changes color by an inter-
`molecular
`reaction. Hydrogen
`peroxide
`facilitates
`the oxidation process, which
`is catalyzed by a num-
`ber of naturally occurring peroxidases
`and catalases
`including
`hemoglobin.
`In the Hemoccult
`test, for
`example, gum guaiac is impregnated
`in a test paper
`and hydrogen
`peroxide
`is provided
`in a developer
`solution. The resultant phenolic oxidation of guaiac
`in the presence of blood yields a blue color (20,23).
`Guaiac is a heterogeneous
`natural product; details of
`the extraction and purification
`technique will there-
`fore influence
`the amount of reagent
`in the test paper
`(34).
`as it passes
`of hemoglobin
`alteration
`Chemical
`through
`the gastrointestinal
`(GI) tract can diminish
`its peroxidaselike
`activity
`and
`render
`stool
`tests
`negative (20,35,36). This is accelerated by pancreatic
`juice and trypsin
`(17,37). Individuals
`vary consider-
`ably in this regard
`(23), so no general
`rule can be
`applied
`to clinical settings. Because of this, however,
`occult upper GI bleeding
`is more likely
`to go unde-
`tected
`than equivalent oozing from the lower gut. In
`the context of screening
`for colorectal
`cancer,
`this is
`an advantage, as it decreases
`the number of positive
`results from other sources.
`
`Commercial Tests
`literally scores of test varia-
`Over the decades
`tions have been described, but only a few commer-
`
`Geneoscopy Exhibit 1033, Page 3
`
`

`

`March
`
`1985
`
`OCCIJLT BLOOD
`
`IN COLORKTAL
`
`CANCER
`
`823
`
`clini-
`in widespread
`are currently
`cial preparations
`cal use. Of these, by far the most popular and the best
`studied
`is Hemoccult.
`This has been available
`for
`more
`than 15 yr; modifications
`around 1977 led to
`the currently distributed Hemoccult
`II slides (Smith-
`Kline Diagnostics, Sunnyvale, Calif.). Each slide con-
`tains two windows of guaiac-impregnated
`paper, on
`which the patient smears a small amount of stool with
`a supplied applicator. This
`is usually
`repeated with
`two subsequent
`bowel movements,
`then
`the
`three-
`slide package
`is returned
`to the
`laboratory. Even a
`single reaction
`among
`the six smears
`is termed a
`positive test on that patient, and further
`investigations
`are advised.
`tests using guaiac
`other commercial
`Numerous
`have been marketed. These include Fecatest
`(Labsys-
`tern Oy, Helsinki, Finland), Quik-Cult
`(Laboratory
`Diagnostics, Morganville, N.J.), ColoScreen
`(Helena
`Laboratories, Beaumont, Tex.), FeCult (Gamma Diag-
`nostica, Houston, Tex.), Colo-Rect
`(Roche Diagnos-
`tics, Nutley, N.J.), Haemoscreen
`(E. Merck Diagnos-
`tica, Darmstadt,
`Federal Republic
`of Germany),
`HemaChek
`(Miles Laboratories,
`Elkhardt,
`Ind.),
`Cameo Pak (Cambridge Chemical Products, Fort Lau-
`derdale, Fla.), and many others. Most are based on
`guaiac-impregnated
`paper, similar to Hemoccult, but
`few have been objectively compared with other tech-
`niques. None has achieved widespread
`popularity.
`The only important
`commercial
`preparation
`based
`on orthotolidine
`is Hematest
`(Miles Larobatories,
`Elkhardt,
`Ind.). Marketed as a tablet with accompa-
`nying
`filter paper,
`it is still widely used by many
`physicians
`and hospitals.
`(Med-Kjemi
`Unlike all of the above, Hemo-Fee
`derivative,
`A/S, H$n, Norway)
`uses a benzidine
`reagent. Mar-
`tetramethylbenzidine,
`as the indicator
`it has under-
`keted
`in the form of cardboard
`slides,
`gone some comparative
`testing
`in Germany
`(38) but
`is not widely popular.
`
`Other Tests
`
`for oc-
`Among the numerous “new” methods
`in the
`cult blood detection
`that continue
`to appear
`literature,
`two are worth noting because
`of their
`potential
`importance:
`assay
`This unique, quantitative
`HemoQuant.
`was recently
`devised
`by Schwartz
`et al. (39a,b).
`Based on
`the conversion
`of heme
`to fluorescent
`porphyrins,
`it is exquisitely
`sensitive, gives virtually
`quantitative
`recovery
`of fecal hemoglobin
`over a
`wide
`range, and
`is unaffected
`by several
`factors
`(discussed
`below)
`that can
`influence Hemoccult,
`including
`stool hydration
`and storage, dietary perox-
`idases,
`iron, and ascorbic
`acid. Moreover, Hemo-
`Quant measures
`not only
`intact heme, but also
`hemoglobin
`already degraded during gut transit (the
`
`(39a,b). Thus, un-
`fraction”)
`converted
`“intestinal
`like other assays,
`it should detect both upper and
`lower GI bleeding with equal sensitivity. Although
`this will probably prove a disadvantage
`for colorec-
`tal screening,
`comparison
`of the converted
`fraction
`with
`total fecal heme could potentially
`provide
`a
`clue to the approximate
`level of a bleeding
`source.
`HemoQuant
`is relatively
`complex
`technically
`and
`has not yet been applied
`to clinical screening
`situa-
`tions. However,
`its quantitative
`capacity and appar-
`ent accuracy
`render
`it an exciting development
`that
`may herald a new era in occult blood detection.
`and
`Immunochemical
`detection. Barrows
`an
`Songster
`and
`their coworkers
`have developed
`that
`immunochemical
`technique
`for occult blood
`shows considerable
`promise
`(40-42).
`It is said
`to
`specifically
`detect human hemoglobin
`free of cross-
`reaction with
`various
`foodstuffs,
`animal
`heme,
`drugs, etc. (4O), and
`the authors have adapted
`the
`technique
`to a relatively
`simple filter paper (“punch
`disc”) suitable
`for clinical screening
`(41,42). A simi-
`lar concept
`is also being developed by others (43,44).
`Immunochemical
`methods
`require
`further valida-
`tion and clinical
`testing, but are a major theoretical
`advance. Specificity
`of the procedure
`is much
`im-
`proved, and dietary and chemical
`restrictions
`for test
`subjects can be eliminated. An additional
`advantage
`is stability
`of the smear
`for up
`to 30 days (42).
`Disadvantages
`include
`a 24-48-h
`delay between
`receiving
`and
`interpreting
`the test (42), as well as
`greater
`technical
`complexity
`and cost compared
`with simpler
`tests. If proven clinically valid,
`immu-
`nochemical methods
`could eventually
`render cur-
`rent occult blood
`techniques
`obsolete.
`
`Blood Loss
`“Normal” Gastrointestinal
`Accuracy of chemical methods
`for the detec-
`tion of fecal blood depends
`on comparison with a
`the late l%Os, quantitation
`“gold standard.” Since
`of ‘lCr-labeled
`red blood cells has been generally
`accepted as the most accurate
`indicator of intestinal
`blood
`loss. Studies with
`this method
`have been
`remarkably
`consistent,
`demonstrating
`“normal”
`blood
`loss of about 0.5-2.0 ml daily (45-48). Hence
`there
`is general agreement
`that
`losses should not
`exceed 2 ml per day, though some accept 3 ml.
`As an aside,
`some authors
`express
`fecal blood
`levels as milligrams of hemoglobin
`per gram of stool
`rather than milliliters of blood per day, because spot
`tests depend upon the concentration
`rather than the
`absolute amount of hemoglobin
`in the stool. The two
`are easily
`compared,
`inasmuch
`as 2 ml/day
`is
`deemed
`equatable with 2 mg of hemoglobin/g
`of
`stool;
`this equivalence,
`though
`crude,
`is based on
`150 g of stool passed per day and a blood hemoglo-
`bin of 15 g/d1 in the average person
`(49).
`
`Geneoscopy Exhibit 1033, Page 4
`
`

`

`824
`
`SIMON
`
`GASTROENTEROLOGY
`
`Vol. 88, No. 3
`
`Specific Test Sensitivities
`
`in this context does not refer to
`“Sensitivity”
`definition noted above, but rather
`the epidemiologic
`to the capacity of a test to detect blood.
`Ostrow and coworkers
`(50) were the first to com-
`pare the sensitivity
`of chemical
`tests directly with
`51Cr-labeling methodology;
`in 1973 they reported an
`unacceptably
`high frequency
`of false-positive
`reac-
`tions with Hematest.
`In contrast, Hemoccult was
`only about one-quarter
`as sensitive but had few false-
`positive
`reactions
`and was highly
`reproducible
`(96%) (50). Other authors of the modern
`era have
`also condemned Hematest as yielding both too many
`false-positive
`(49-52) and too many
`false-negative
`(50,53) results. The test is also poorly
`reproducible
`and there is remarkably high discordance
`in interob-
`server readings of the results (50). Hematest
`is there-
`fore clearly unreliable
`and should be abandoned
`as a
`test for fecal occult blood.
`give far
`preparations
`Liquid quaiac or benzidine
`too many false-positive
`results for valid clinical use
`(20,49-53). Hemoccult
`fares much better, primarily
`because of its lesser sensitivity;
`in objective compari-
`sons with “Cr-labeled
`red blood cell
`losses, only
`-7%-12% falsely positive
`results are generally
`re-
`corded (4954). This is at the price of missing patho-
`logic amounts
`of blood, however. A number
`of
`studies have shown a high proportion
`of negative
`Hemoccult
`reactions when bleeding
`is in the 5-10
`ml/day
`range
`(38,49,50,54-56),
`and
`losses >20
`ml/day are necessary
`to achieve 80%-90% Hemoc-
`cult positivity
`(49,54,55).
`Indeed, Heinrich and Ica-
`gic (38) found
`that Hemoccult
`not uncommonly
`missed 40 ml/day,
`though
`this is contrary
`to all other
`studies.
`sensitivity
`that Hemoccult
`indicate
`In vitro studies
`influenced
`by seemingly minor
`can be markedly
`technical
`factors such as the matrix
`in which hemo-
`globin
`is contained
`and whether
`the red cells are
`lysed or intact
`(57). Moreover,
`sensitivity
`of the
`commercial
`test has apparently
`changed over
`the
`years (58), and the currently marketed Hemoccult
`II
`seems more sensitive
`than some of the older prepara-
`tions on which the above data are based (1959). This
`has actually affected
`the rate of positivity
`and the
`predictive
`value of the
`test
`in clinical
`screening
`situations (16,19,60). Because formal studies directly
`comparing Hemoccult with Hemoccult
`II results
`have never been published,
`the sensitivity
`data de-
`rived on the 1970s cannot be assumed
`applicable
`today.
`is avail-
`information
`comparative
`limited
`Only
`able on other commercial
`tests. Both Fecatest and
`Colo-Rect appear
`to be more sensitive
`than Hemoc-
`cult (38,561, and Hemo-Fee
`less sensitive (38). How-
`ever, some comparative
`results have been challenged
`
`in
`in a lively debate
`resulting
`on technical grounds,
`the literature (58,61). From a review of the evidence
`it is clear that sensitivity
`data must be determined
`independently
`for each commercial
`test. Results on
`one preparation
`cannot be extrapolated
`to another,
`even
`if based on the same reagent and appearing
`essentially
`similar.
`
`Technical Factors Influencing the
`Reaction
`
`that the seem-
`indicates
`The above discussion
`ingly “simple”
`occult blood
`reaction
`is actually
`highly complex. Other
`technical
`issues complicate
`the situation
`even further. A number of these have
`clinical
`implications,
`but unfortunately
`the
`litera-
`ture is a morass of often conflicting
`information.
`
`Dietary Peroxidases
`
`for
`is not specific
`reaction
`The occult blood
`is affected by peroxidases
`human hemoglobin
`but
`and catalases
`in various foodstuffs
`including
`red and
`white meats, fish, fresh fruits, and uncooked vegeta-
`important
`this
`is for clinical
`bles (20,23,62). How
`screening
`is debated. Greegor (63), the first physician
`to report the use of Hemoccult, noted that a meat-free
`diet cut down the number of positive reactions
`in his
`clinical practice. Ever since, his dietary advice has
`been followed by a number of authors,
`including
`the
`group at the Sloan-Kettering
`Institute who are lead-
`ers in the study of colorectal cancer (19). Many other
`authors,
`however,
`ignore diet
`in
`their
`screening
`programs
`(see Table 1). This makes comparison
`of
`clinical studies difficult.
`A controlled
`trial on this point has never been
`carried
`out,
`and
`the
`available
`data
`differ
`(17,50,64,65). The most carefully
`designed
`dietary
`study was recently
`reported
`by Macrae and col-
`leagues (66). Using Hemoccult
`II, they concluded
`that positive
`results on an unrestricted
`diet deserve
`investigation
`if the test slides are not hydrated, but
`that red meat in the diet is unacceptable
`if the slides
`are rehydrated
`(66). Rehydration
`of slides as a tech-
`nical
`factor
`in test positivity
`is discussed
`further
`below.
`a
`to establish whether
`trials are needed
`Clinical
`low-peroxidase
`diet
`is justified
`for screening
`pro-
`grams; on present evidence
`this remains uncertain.
`It
`is worth stressing, however,
`that even a minor diet-
`related
`decrease
`in false-positive
`results may be
`clinically
`important. This is because a small increase
`in specificity can have a major impact on the predic-
`tive value of a positive
`test (8), thereby diminishing
`needless
`investigations
`on healthy
`people
`(see
`above).
`
`Geneoscopy Exhibit 1033, Page 5
`
`

`

`March 1985
`
`OCCULT BLOOD IN COLORECTAL CANCER
`
`825
`
`Dietary Residue
`
`to argu-
`factor open
`is another dietary
`This
`ment. Credit or blame again goes to Greegor (63),
`who arbitrarily put his patients on a high-residue
`(in
`addition
`to meat-free)
`diet. His rationale was “to
`guard against
`the unwitting use of a too bland diet”
`and
`to help ensure bleeding
`from any colorectal
`lesion present (63). Use of this dietary advice has
`been widely adopted, but as pointed out by O&row
`Indeed high-roughage
`(67), has never been validated.
`intake
`theoretically
`could have two unfavorable
`ef-
`fects on occult blood screening:
`its high peroxidase
`content might
`increase
`the number of false-positive
`tests, and its high bulk might dilute any fecal hemo-
`(67). These
`globin
`to undetectable
`concentrations
`points have not been subjected
`to proper
`testing,
`though Hellerstein
`et al. (68) found
`that a high-fiber
`diet did not enhance bleeding
`from colonic polyps.
`On available evidence,
`use of a high-residue
`diet
`for occult blood
`testing appears arbitrary and with-
`out scientific validation.
`
`(57). In
`results
`the number of false-positive
`increase
`of all Hemoc-
`fact, rehydration
`increases
`sensitivity
`cult II slides, not just those stored for several days,
`and this does produce more false-positive
`readings
`(73).
`results
`clinical
`explain
`This point can probably
`program,
`in
`screening
`from
`the Sloan-Kettering
`which hydration
`of Hemoccult
`II slides
`increased
`overall screening positivity
`from 3.7% to 5.4% (16).
`Unfortunately
`but not surprisingly,
`this was accom-
`panied by a sharply decreased
`predictive
`value for
`from 44% to only 19% (16). Thus
`the
`neoplasia
`benefit of slide hydration
`is probably outweighed
`by
`an unacceptable
`decrease
`in test specificity. Ma-
`crae’s dietary studies cited above (66) suggest that a
`strict meat-free diet may minimize
`the problem, but
`this remains
`to be tested
`in clinical
`trials.
`It is apparent
`from
`these data
`that storage and
`hydration
`of Hemoccult
`slides can have an impor-
`tant impact on clinical
`screening programs, but the
`optimal clinical application
`of these variables
`is not
`yet clear.
`
`Slide Storage and Rehydration
`
`Drugs
`
`that 14% of
`In 1976 Morris et al. (49) noted
`positive Hemoccult
`results on fresh stool became
`negative after the slides were
`left at room tempera-
`ture for 2 days. Subsequent
`authors have confirmed
`this tendency (69,703. Though some of the data have
`been criticized
`(711, it appears
`that weakly positive
`Hemoccult
`reactions may yield negative or equivocal
`results after 2-4 days of storage, whereas
`a strong
`reaction will remain positive
`for at least 10 days (57).
`Reasons
`for this storage artifact are uncertain. The
`problem
`is not fading of the color reaction per se, but
`presumably
`dessication
`of stool on the slide over a
`period of time
`(71). Precisely
`how
`this alters
`the
`chemical
`reaction
`has not been ascertained.
`Tests
`that fade may mainly be falsely positive anyway (7l),
`but this requires
`substantiation.
`inasmuch
`The clinical
`implications
`are obvious,
`to collect
`as it is common practice
`for the patient
`the
`test
`three consecutive
`stools before
`returning
`slides
`to the physician,
`often by mail. Thus artifac-
`tually negative
`results due to storage might seriously
`impair
`the value of screening programs.
`To help solve this problem, Wells and Pagan0 (72)
`suggested
`rehydration
`of Hemoccult
`slides with a
`drop of water before
`testing. This presumably
`assists
`dissolution
`of dessicated hemoglobin
`(57) and might
`also lyse red cells with release of free hemoglobin
`clearly does enhance
`sensitivity
`of
`(73). Hydration
`the Hemoccult
`test and restores positive
`reactions
`(57,72,73). The question,
`though,
`is whether
`it en-
`hances sensitivity
`too much. A variety of interfering
`peroxidases
`are presumably
`also reactivated
`and can
`
`the occult
`A number of drugs can influence
`blood reaction. The clinical potential of this is self-
`evident.
`been
`have
`preparations
`iron
`Iron. Oral
`tests for over
`blamed
`for producing
`falsely positive
`half a century,
`though
`a number of authors have
`disputed
`this (reviewed
`in References
`20 and 74).
`Lifton and Kreiser
`(74) recently
`documented
`that
`ferrous sulfate and ferrous gluconate produce a high
`number
`of positive
`reactions
`in healthy
`subjects.
`Though
`these
`results
`could conceivably
`represent
`true positives
`due
`to GI mucosal
`irritation
`(75),
`ferrous
`salts
`in vitro also give positive Hemoccult
`reactions
`(74). In either case, it seems wise to avoid
`oral iron compounds
`before occult blood
`testing.
`to
`Aspirin. Aspirin
`is a well-known
`irritant
`the GI tract and is commonly blamed for inducing GI
`(76). Studies with 5’Cr have docu-
`hemorrhage
`mented
`that
`the drug
`increases
`fecal blood
`loss in
`healthy
`subjects,
`though usually by only a small
`amount (77,78). Because of this,
`it is commonly
`believed
`that acetylsalicylic
`acid can produce posi-
`tive occult blood tests in the absence of GI pathology.
`Some new evidence,
`however.
`casts doubt on this
`(55,68,79), and the problem
`is probably not as impor-
`tant as feared. Nevertheless,
`it seems wise to inter-
`dict acetylsalicylic
`acid before occult blood testing if
`possible. Aspirin
`ingestors with positive
`results
`should probably be retested before colonic
`investiga-
`tions are undertaken,
`because
`the likelihood
`of tu-
`mor is reportedly
`not increased unless
`tests remain
`positive after the drug is stopped (80).
`
`Geneoscopy Exhibit 1033, Page 6
`
`

`

`826 SIMON
`
`GASTROENTEROLOGY Vol. 88, No. 3
`
`Ascorbic acid. This vitamin acts as an antiox-
`idant and therefore
`interferes with the pseudoperox-
`idase
`reaction,
`yielding
`falsely
`negative
`results
`(81,821. This could be bothersome
`in view of the
`recent
`fad for high-dose
`ascorbic acid
`ingestion
`to
`ward off colds and other diseases.
`produce
`may
`Miscellaneous.
`Cimetidine
`in gastric aspi-
`falsely positive Hemoccult
`reactions
`rates (83-85), but this does not appear
`to be the case
`in stool specimens
`(86,87); hence on current
`evi-
`dence this widely prescribed drug need not be feared
`in fecal occult blood
`studies. Povidone
`iodine,
`a
`surgical antiseptic, will produce positive
`reactions
`due
`to
`the strong oxidative
`properties
`of iodine
`(88,89). Barium
`sulfate
`in the stool after GI x-ray
`examinations
`does not influence
`the reaction
`(491,
`but laxatives may tend to diminish both false-posi-
`tive and
`false-negative
`results
`(49). The possible
`influence
`of laxatives
`deserves
`further
`study. The
`long-standing
`belief that falsely positive guaiac tests
`can be produced
`by glyceryl guaiacolate
`(guaifene-
`sin), a common
`cough medicine,
`has now been
`refuted
`(90,91). Finally,
`if stool specimens
`are pre-
`served
`in formalin, a falsely positive benzidine
`reac-
`tion may result (92).
`factors can
`In summary,
`a number of technical
`affect the clinical
`reliability of occult blood tests, yet
`considerable
`confusion
`still permeates
`the literature
`on many of these factors. Further clinical observa-
`tions, especially well-designed
`controlled
`studies,
`may clarify
`some of the
`issues. However,
`greater
`hope probably
`lies in the evolution of better screen-
`ing tests that are less subject to technical artifacts, for
`example,
`the
`immunochemical
`assays mentioned
`earlier (40-44).
`
`in Known Colorectal
`
`Occult Bleeding
`Tumors
`Reasons for Falsely Negative Tests
`Earlier discussion emphasized
`falsely positive
`occult blood tests. Equally
`important
`is the problem
`of an unreactive
`test despite
`the presence of colonic
`neoplasm. This can occur for at least three reasons.
`Test
`insensitivity.
`As noted
`above,
`fecal
`losses exceeding
`-20 ml/day are needed
`for
`blood
`reliably positive Hemoccult
`reactions
`(38,49,54,55).
`Hence
`losses up to ten times “normal,”
`and occa-
`sionally even more, can be missed. A rarer technical
`cause of false negativity
`is vitamin C ingestion
`(81,82), also noted above.
`Non-bleeding
`of the
`have
`tumor. Clinicians
`long known
`that bowel cancers do not always bleed,
`yet surprisingly
`few quantitative
`data are available
`on this point. Doran and Hardcastle
`(55) recently
`documented
`large daily
`fluctuations
`from 0 to 75
`
`ml/day in individual patients; values exceeded 10 ml
`in fewer
`than 25% of all daily collections. Macrae
`and St. John
`(73) also
`recorded
`highly
`variable
`-9 ml/day
`for right-sided
`losses, averaging
`only
`lesions
`and <2 ml/day
`in
`left-sided
`carcinomas.
`Benign colonic polyps bleed even
`less (48,73). Re-
`cent colonoscopic
`correlations
`suggest further
`that
`only ulcerated
`tumors bleed
`(93,94). This
`is not
`surprising
`and
`is probably
`another
`reason
`for the
`absence of detectable blood with many neoplasms.
`Chromium
`5lichemical
`disparities. Occult
`is not uniformly
`distributed
`in feces, even
`if
`blood
`from an upper
`intestinal
`source
`(95); small stool
`samples
`can
`therefore
`test negative
`even
`though
`blood
`is readily demonstrable
`in other portions. By
`the same token, a single drop of blood from a low
`colorectal
`lesion will be detected
`by Hemoccult
`smear but not by abnormal 51Cr-labeled
`red blood
`cell counts
`in the total stool (73). Radioassay might
`also detect
`labeled
`red cell debris not containing
`hemoglobin
`(34). Finally, hemoglobin
`degradation
`along
`the gut weakens
`pseudoperoxidase
`activity
`with resultant diminution
`of the chemical
`reaction
`(see above) but without
`loss of radioactivity.
`For
`these
`reasons
`comparison
`of chemical
`techniques
`with 51Cr data is not always valid (34,73).
`
`Clinical Findings
`
`it is not surprising
`In view of the above points,
`a
`that clinical
`studies have repeatedly
`documented
`high proportion
`of negative
`tests
`in known bowel
`cancer.
`Indeed, modern
`figures show positive He-
`moccult
`reactions
`in only
`-50%66%
`of patients
`with proven malignancy
`(41,55,73,94,96). Results
`are more
`likely
`to be negative
`in left-sided
`than
`in
`right-sided
`lesions
`(41,73,94), perhaps
`because of
`higher average blood
`losses
`from cancers
`in
`the
`colon (73). Negative Hemoc-
`cecum and ascending
`cult tests are even more common with benign colon-
`ic adenomas. Macrae and St. John (73) found
`that
`only polyps
`larger
`than 2 cm produced
`detectable
`bleeding, and several authors have reported negative
`Hemoccult
`reactions
`in >75% of patients with endo-
`scopically proven adenomas
`(16,47,94,97).
`tumor
`Increasing
`the number
`of tests on each
`patient will enhance
`the yield. Early on, Greegor (63)
`advised six Hemoccult
`smears on each subject, rep-
`resenting
`two separate portions of three consecutive
`bowel motions. This number has been widely adopt-
`ed, even though arbitrarily
`determined.
`Several au-
`thors have documented
`that this does
`increase
`the
`yield over single
`testing
`(19,73,98), and the three-
`stool, six-smear Greegor program probably offers a
`reasonable
`compromise
`between
`undue
`inconve-
`nience
`and undue
`false negativity. As discussed
`
`Geneoscopy Exhibit 1033, Page 7
`
`

`

`March
`
`1985
`
`OCCULT BLOOD
`
`IN COLOKECTAI,
`
`CANCER
`
`827
`
`from a cost-
`this is optimal
`later, however, whether
`benefit point of view is another question.
`of
`The yield can also be increased by rehydration
`Hemoccult
`slides before addition of the test reagent
`(73). This decreases
`specificity (16,73), however, and
`on balance, slide hydration
`is probably not advisable
`(see above].
`for
`import
`results have major
`The above-noted
`is
`programs. The implication
`population
`screening
`that at least 33%, and perhaps 50%, of colorectal
`cancers
`in the screened population will be missed.
`In fact, the figure may be even higher
`than
`this
`if
`subclinical
`cancers bleed
`less than the symptomatic
`growths
`from which
`the above data were derived.
`Thus
`the sensitivity
`(in the epidemiologic
`defini-
`tion] of occult blood
`testing
`is actually quite
`low,
`in the 50°h-650h range. This
`impor-
`probably on