Nonuniform Distribution of Occult Blood in Feces
RICHARD E. ROSENFIELD, M.D., SHAUL KOCHWA, PH.D.,
KACZERA,
Rosenfield, Richard E., Kochwa, Shaul, Kaczera, Zygmunt,
and Maimon, Jonathan: Nonuniform distribution of occult
blood in feces. Am J Clin Pathol 71: 204-209, Inhibition of
anti-Rh29 by erythrocytic stroma in feces was devised as a
specific test for fecal occult blood. The sensitivity of this test
was equivalent to that of a standard Hemoccult® test, namely,
108 erythrocytes/g feces. Comparison of results of this test with
results of Hemoccult tests of random stool specimens and of
stools following ingestion of autologous blood revealed nonuniform distribution of occult blood in feces. The extent of nonuniformity was determined by testing samples of stool specimens following ingestion of 51Cr-labeled autologous blood. This
allowed comparison of Hemoccult, inhibition of anti-Rh, and
radioactivity, and showed that the three labels could separate
in the feces and that some single small samples of feces could
be relatively free of blood while blood was readily demonstrable
in other portions. The variability of a standard Hemoccult test
was somewhat reduced by dispersing the feces in distilled water
before performing the test. (Key words: Fecal occult blood.)
Department of Pathology, Mount Sinai School of
Medicine, City University of New York, New York
FECAL OCCULT BLOOD has long been detected by
chemical tests of stool for peroxidase activity. These
tests, however, are subject to false-positive results
from ingested animal and plant peroxidases or peroxidaselike substances." This has led to use of meat-free
diets to reduce the incidence of false-positive results. 3
The problems inherent with these tests have been reviewed, 15,18 and many causes of both false-positive14
and false-negative 813 results have been described.
It is known from 51 Cr-labeled autologous blood studies that 2 - 4 ml of blood may be lost in the feces daily. 1,2
Thus, bleeding in excess of this amount should represent pathologic fecal occult blood. In the last decade, a
commercial product (Hemoccult®*) consisting of stable , dried, guaiac-impregnated filter paper has provided
this degree of sensitivity, and has been associated
with a relatively low incidence of false-positive
reactions. 7,11,13,17
Consideration of population screening tests for the
early detection of colonic malignancy has generated
Received October 20, 1977; received revised manuscript and
accepted for publication December 27, 1977.
Supported by Contract NO1-CB-43870 from National Cancer
Institute, NIH, Bethesda, Maryland.
Address reprint requests to Dr. Rosenfield: Director, Department
of Blood Bank and Clinical Microscopy, The Mount Sinai Hospital,
Professor of Pathology, Mount Sinai School of Medicine, City
University of New York, 1176 Fifth Avenue, New York, New
York 10029.
* Smith Kline Diagnostics, Division of Smith Kline Corporation,
Philadelphia, Pennsylvania.
PH.D.,
AND JONATHAN MAIMON, M.S.
new interest in tests for fecal occult blood. 15,17 To overcome problems posed by intermittent gastrointestinal
blood loss and nonhomogeneity of shed blood in feces,
three daily tests for blood in stool specimens have been
recommended. 315 Since a positive screening test for
fecal occult blood leads to costly colonic and radiologic
evaluations, a more specific test for occult human blood
in human feces was sought. Meat-free diets to reduce
the false-positive results of chemical tests and the intravenous administration of 51Cr-labeled autologous
blood generally were considered to be unacceptable for
mass screening programs.
Blood provides a wide variety of protein and cellular
antigens that carry identifiable antigenic products. Feces, however, consists of particulate matter, cells, bacteria, and viruses, and contains numerous enzymes
such as proteases, lipases, and neuraminidases of both
endogenous and exogenous origin. These should, and
do, have deleterious effects on human blood elements
that carry recognizable antigens.
Despite these problems, a serologic test for human
blood in human feces was constructed. It consisted of
attempting to neutralize Rh antibody with hypotonically
treated stool samples after differential centrifugation,
first to eliminate large particles and then to recover
small ones such as bacteria and erythrocytic ghosts.
The Rh specificity used was Rh29, an antigen possessed
almost universally, being absent only in the extremely
rare Rhnun blood type. 4 Rh29, like other Rh antigens,
is expressed only on erythrocytic membranes and not
on other cells. 12 Except for a very few nonhuman primates, Rh does not occur in other species. 12 Results
of this test were compared with results of both standard Hemoccult tests and Hemoccult tests performed
on stool samples dispersed in distilled water.
0002-9173/79/0200/0204 $00.80 © Ai
204
Materials and Methods
(I) Bovine Serum Albumin (BSA). Powdered bovine
serum albumin! was dissolved in 2% concentration in
t Armour Pharmaceutical Co., Chicago, Illinois,
n Society of Clinical Pathologists
NONUNIFORM DISTRIBUTION OF OCCULT BLOOD IN FECES
Vol. 71 . No. 2
0.9% NaCl. This solution was stored at 4 C for as long
as a month before use.
(2) Anti-Rh29. The serum of Mrs. J.R.B. was used. 4
(3) Anti-Rhl. The serum of Mrs. F. was used. 10
(4) Radioactivity
Measurements.
Measurements
were made with a Wallac 500$ gamma counter equipped
with a 3-inch beryllium-coated crystal.
m
I-Labeling
of
Erythrocytes
A mixture was prepared with 100 p\ 0.1 N HC1, 200
(JL\ 0.6 M NaCl, 2 pi 0.02 M IC1 solution, and 5 pi 125I
(0.5 mCi).§ This solution was stable, but after the addition of 50 juJ 1 M glycine buffer, pH 9.0, it was used
immediately (solution A). A 10% suspension (0.4 ml)
of washed erythrocytes in 0.9% NaCl was added to
solution A and incubated at room temperature for 3 min
with gentle swirling. Another freshly prepared solution
A was then added, after which the erythrocytes were
centrifuged and washed repeatedly with 0.9% NaCl
until the washings were free of radioactivity.
il
Cr-Labeled
Erythrocytes for
Ingestion
Twenty-five milliliters of sterile A . C D . blood were
labeled with 60 pCi 51Cr as sodium chromate. 9,1 ' Ten
milliliters of packed erythrocytes from this labeled
blood were washed six times, mixed with 100 ml of
grape juice, and swallowed.
Stool
Specimens
Feces, usually the total for one day, were collected
without preservative and processed on the same day.
An occasional specimen was stored at 4 C overnight
before processing.
Fractionation of Stool
Specimens
Specimens (0.5 or 1.0 g) of feces were dispersed with
wooden applicator sticks in ten volumes of distilled
water. Large heavy particles were sedimented either
by gravity (for 15 or 30 min) or, preferentially, by centrifugation at ~ 50 x g for 5 min (500 rpm in a Sorval
GLC-1 centrifuge).** This material is referred to as "50
x g sediment." The supernatant fluid from this separation
was then sedimented at 27,000 x g( 15,000 rpm in a Sorval
RC-5 refrigerated centrifuge) for 30 min at 4 C, a procedure known to sediment erythrocytic stroma. 10 This
sediment is referred to as "final pellet," and the supernatant fluid as "final supernatant." An alternative, simpler, and faster preparation of "final pellet" was deli LKB, Stockholm, Sweden.
§ Amersham-Searle, Des Plaines, Illinois.
' Mallinckrodt, St. Louis, Missouri.
** Ivan Sorval, Norwalk, Connecticut.
205
125
Table 1. Percentage of Recovery of I-labeled Stroma
from Feces—Comparison of Three Methods
to Remove Heavy Stool Particles
Erythrocytes Added to Feces
Method to Remove
Heavy Particles
1.03 x 109
1.30 x 108
4.00 x 10'
50 x g
15 minutes settling
30 minutes settling
86
96
90
81
96
85
86
90
98
vised later. This consisted of centrifugation of 0.5-ml
volumes of the 50 x g supernatant fluid at —12,000
x g for 15 min in a Beckman-Spinco Microfuge.tt
Final pellets thus obtained were adequate for single serologic tests and were fully as reliable as material sedimented at 27,000 x g. Final pellets were resuspended
in a volume of 0.9% NaCl that corresponded to the
volume (or weight) of the sample of stool from which
they had been obtained.
Recovery of
l25
I-Labeled
Stroma
The efficiency of recovery of known erythrocytic
stroma was determined by preparing artificial mixtures.
Three 1-g aliquots of Hemoccult-negative stool were
mixed with 107, 108, and 109 erythrocytes. Each aliquot
also received 3 x 107 of 125I-labeled erythrocytes. Final
pellets were counted for recovery of labeled stroma, and
the percentage of recovery was adjusted to total radioactivity precipitated by trichloracetic acid. The results,
shown in Table 1, indicate approximately 90% recovery.
Hemoccult
tests.
Stool specimens were tested for occult blood with
Hemoccult slides by the use of the standard method
described by the manufacturer.
"Hemoccult-Water"
Test
One gram of feces was dispersed in 10 ml of distilled
water and homogenized with an applicator stick. A
drop of the suspension was tested on a Hemoccult
slide as described by the manufacturer.
Serologic Tests for Rh in Stool Pellets
Two Rh specificities were studied for the capacity of
erythrocytes in feces to inhibit or neutralize Rh antibody. In each case, the anti-Rh was diluted in 2% BSA
so that it would modestly agglutinate ficin-treated Rhpositive erythrocytes. 5 For this test equal volumes of
diluted anti-Rh and a 2% suspension of erythrocytes in
t t Spinco, Palo Alto, California.
A.J.C.P. • February 1979
ROS ENFIELD ET AL.
206
Table 2, Detection of Blood in Artificial Mixtures of Erythrocytes in Feces
Erythrocytes/g Stool1
6
107
108
Test
RBC Used
0
10
Hemoccult-water
Rh antibody neutralization
Anti-Rhl
Rh:l or Rh: - 1
Negative
Negative
Trace
Moderate
Strong
Rh:l
Rh:- 1
Rh:l or Rh: - 1
Negative
Negative
Negative
Negative
Negative
Negative
Doubtful
Negative
Doubtful
Moderate
Negative
Moderate
Strong
Negative
Strong
Anti-Rh29
0.9% NaCl were mixed, incubated for 15 min at 37 C,
and briefly centrifuged (1,000 x g for 10 sec).tt The
extent of agglutination used was + + + (numerous large
clumps of cells) on a scale ranging from + (very weak
but discernible agglutination under x6 magnification)
to + + + + (solid agglutination, all cells in one clump
after gentle shaking). One of the antisera used was
anti-Rh29; the other was anti-Rhl (Rh0 or D).
Stool specimens from normal volunteer subjects,
found to be free of blood by repeated standard Hemoccult tests, were used for evaluation. From each specimen, five 1-g aliquots were prepared. One of these was
untreated, while the others were mixed with 0.1 ml of a
cell suspension in 0.9% NaCl that contained 106, 107,
108, or 109 erythrocytes/ml. The last was essentially
0.1 ml packed cells. After the suspension was mixed
with wooden applicator sticks, a 10-ml volume of distilled water was added, and each stool sample was
tested by Hemoccult-water test and then processed to
prepare final pellets. To 0.1 ml of each final pellet suspension, 0.1 ml diluted anti-Rh was added. Additionally,
0.1 ml anti-Rh was mixed with 0.1 ml packed erythrocytes (109 erythrocytes) and another 0.1 ml antibody
was mixed with 0.1 ml 0.9% NaCl. All seven antibody
mixtures were incubated at 37 C for an hour and centrifuged at —12,000 x g for 4 min. One drop of each
supernatant fluid was then added to one drop of a 2%
suspension of ficin-treated erythrocytes to test for residual antibody activity.
Distribution of Swallowed Blood in Stool
To assay the distribution of swallowed blood in feces,
feces were collected daily for five days from a volunteer
who swallowed 10 ml of autologous, washed, packed
erythrocytes labeled with 51Cr9 to carry 3.2 x 106cpm.
All stool samples were weighed, and 1-g portions were
prepared from each. Twenty such portions were prepared on day 1, and ten each were prepared on days
2 and 3. All were tested as follows: (a) standard Hemoccult; (b) radioactivity and Hemoccult-water test after
dispersal of the sample in distilled water; (c) radioactivtt Serofuge, Clay Adams Co., Division of Becton, Dickinson
and Co., Parsippany, New Jersey.
10"
ity of 50 g sediment; (d) radioactivity of final pellet.
The capability of the final pellet to neutralize anti-Rh29
was assayed in eight of the 20 samples of the first
day's specimen and all samples of the second and third'
days' specimens.
The format of analysis allowed for the detection of
three independent markers: peroxidase activity by two
differing Hemoccult tests, erythrocytic membrane Rh
antigen activity by neutralization of anti-Rh29, and
51
Cr-labeled j3 chains of hemoglobin by radioactivity,
the latter adjusted as required by the geometry of counting. In addition, the distributions of radioactivity in the
50 x g sediment, final pellet, and final supernatant were
calculated.
Results
Serologic Testing for Blood in Artificial Mixtures of
Erythrocytes in Stool
When artificial mixtures of erythrocytes in stool were
prepared as described in Materials and Methods, the
stool samples dispersed in distilled water were consistently positive by Hemoccult in accordance with the
number of erythrocytes added to the 1-g stool sample.
Final pellets of these samples, when incubated with
anti-Rh, neutralized agglutinating activity in similar accordance with numbers of added erythrocytes.
Typical results are shown in Table 2, where either
Rh: 1 (Rh0 or D positive) or Rh:-1 erythrocytes added
to feces neutralized anti-Rh29, but only Rh: 1 cells neutralized anti-Rhl. Complete neutralization was observed with 109 erythrocytes/g feces, and almost complete neutralization with 10* erythrocytes. Doubtful
neutralization was seen with 107 erythrocytes, and no
neutralization could be detected with 106 erythrocytes/g feces. Parallel Hemoccult tests of the same
well-mixed feces at 1:10 concentration in distilled water
were negative with 106 erythrocytes/g feces, trace positive with 107 erythrocytes, moderately positive with 108
erythrocytes, and strongly positive with 109 erythrocytes/g feces.
The results portrayed in Table 2 were very reproducible for freshly prepared mixtures of erythrocytes in
feces. However, when artificial mixtures of erythro-
Vol.71 • No. 2
207
NONUNIFORM DISTRIBUTION OF OCCULT BLOOD IN FECES
cytes in feces were incubated at 37 C, serologic ability
to neutralize anti-Rh was present at 24 hours, but absent after 48 hours unless 0.1% sodium azide was included as a preservative. With added sodium azide,
Rh antigenic activity was preserved at 37 C for as long
as five days.
False-positive and False-negative
Fecal Occult Blood
Results of Tests for
Neither meat nor animal blood inhibited anti-Rh, but
both caused positive Hemoccult tests. However, when
a normal volunteer deliberately ate as much as 1 kg of
very rare beef, standard Hemoccult tests were negative.
Hemoccult tests of feces in distilled water were only
faintly positive after ingestion of 1 kg of beef and were
negative after ingestion of only 500 g.
As reported, 14 scraped tomato skin, but not tomato
pulp, was found Hemoccult-positive. Also as reported, 8
ascorbic acid in stool was found to abolish a known
positive Hemoccult test, but did so only at a level of at
least 5 mg/g feces and only when the pH of the stool
was less than 7.0. Indeed, when the pH was less than
5.0, even the inhibition of anti-Rh was reduced because, as reported, 10 the Rh antigens of erythrocytic
stroma are totally destroyed at low pH. Such low pH
values, however, seem rather unlikely to occur in feces.
Unreliability of Tests for Occult Blood in
Stool Specimens
Stool specimens obtained from more than a hundred
unselected patients were tested for blood both by the
standard Hemoccult method and by determination of
the capacity of the final pellet material to inhibit antiRh29. Whenever these tests were performed, artificial
mixtures of blood in Hemoccult-negative feces from
the volunteer were prepared and tested as standards
known to contain 0, 107, 108, 109 erythrocytes/g feces.
Although these standards always provided parallel and
concordant results between Hemoccult-water tests
and Rh serology tests, very few patient samples were
in agreement for both Rh serology and the standard
Hemoccult test. The results are summarized in Table 3,
where, of 18 stool samples found positive by either
test, only three were equally positive by both. Indeed,
four samples were strongly positive by Rh serology and
negative by standard Hemoccult test, while six others
were strongly positive by the standard Hemoccult test
but negative by Rh serology.
A volunteer swallowed autologous blood and collected stool specimens for four subsequent days to provide feces that might contain blood and permit a more
valid comparison of the two test procedures. Two experiments were performed. In one, the volunteer swal-
Table 3. Results of Tests for Occult Blood in
Unselected Patient Stool Samples
Number of Patients
Hemoccult
Serology
3
1
4
4
6
>100
+
+
±
+
+
±
+
+
-
+ = strongly positive.
± - weakly positive.
- - negative.
lowed 10 ml of blood, and concordant positive results
were obtained on the second and third days after blood
ingestion. In the other experiment, a 20-ml volume
of blood was swallowed, and concordant results were
observed on the second postingestion day. In both experiments, stools on subsequent days were negative by
both tests, and in both experiments stools on day one
were discordantly positive. After ingestion of 10 ml
of blood, the first day's stool was standard Hemoccultpositive but negative by Rh serology; after 20 ml the
reverse was observed: the standard Hemoccult test was
negative, but the Rh serologic test was positive.
Autologous Ingested Blood in Stool: Distribution of
Three Independent Markers
To determine the uniformity of the distribution of
ingested blood in feces, a volunteer swallowed 10 ml of
packed autologous erythrocytes previously labeled
with 51Cr. The details of the experiment are given in
Materials and Methods.
Table 4 summarizes the average percentage of distribution of 51Cr in 50 x g sediments, final pellets, and
final supernatants for all three days of stool collection,
during which time frame approximately 90% of total
radioactivity was recovered in the stools. As expected,
relatively little radioactivity was recovered in
final pellets where erythrocytic membranes were collected; erythrocytic membranes accept rather little
chromation, more than 90% binding to the /3 chains
of hemoglobin. 6 An increase from 8.9% on day 1 to
18.9% on day 3 was observed, and might have indicated increasing adsorbance of hemoglobin or hemoglobin fragments by bacteria. Such adsorbance had obviously occurred on larger fibers and cellular particles
because the 50 x g sediments carried about 40% of total
radioactivity on all three days. As shown in Table 1,
stroma labeled with 125I were not sequestered to such
an extent of the 50 x g sediment but were found in 90%
concentration in the final pellet. Very few final supernatants contained more than 50% of total radioactivity.
Table 4 also summarizes the distributions of radioactivity in the various aliquots assayed on each day.
R0SENFIELD£7"/1L.
208
Table 4. Distribution of 51Cr within Stool Specimens
Total, expressed as 1010
erythrocytes
Mean
Standard deviation
Coefficient of variation
Percentage within portion of
specimen
50 x g sediment
Mean
Standard deviation
Final pellet
Mean
Standard deviation
Final supernatant
Mean
Standard deviation
Day 1
(n = 20)
Day 2
(n = 10)
Day 3
(n = 10)
5.2411
1.3194
25.2
3.1973
0.7791
24.4
0.9000
1.1054
122.8
39.1
1.94
41.1
2.55
42.4
2.35
8.9
1.32
15.2
1.38
18.9
4.1
52.0
1.97
43.7
1.80
38.7
3.06
Standard deviations of these samples, expressed as
coefficients of variation, were about 25% on days 1 and
2, and 123% on day 3. Thus, radioactivity of labeled
swallowed blood was not distributed uniformly in the
feces.
Table 5, summarizes the comparisons of all positive
tests for blood in feces. Since all stool samples contained some 51Cr, adjusted radioactivity was scored as
positive only when it indicated the presence of S3
x 107 erythrocytes/g feces. Here, too, marked variations were observed, especially on day 3. But even on
days 1 and 2 little more than half the samples were
positive by all four tests. On days 1 and 2, radioactivity
and the Hemoccult test of stool in distilled water were
the most efficient tests, and inhibition of anti-Rh29 appeared to be only 50% as efficient. On day 3, however,
Rh serology was the best test, providing 50% detection,
while the other three tests were less efficient.
The semiquantitative interpretations of both Hemoccult results and the inhibition observed in inhibition tests
of anti-Rh29 were ranked and, with the ranks of total
radioactivity, Spearman's rank correlation coefficients
(rs) were employed to find significant correlations between any two tests. This statistical analysis is not
shown in the tables. In six comparisons of paired
strengths of reactions on three days of stool collection,
no significant correlation was found on days two and
three (P > 0.05). On day 1 the standard Hemoccult
test versus the Hemoccult-water test and the standard
Hemoccult test versus radioactivity correlated, P
= 0.03 and 0.005, respectively.
Discussion
Specimens of stool vary in consistency and quantity.
They contain undigested matter in the form of fibers
and clumps of cellular particles. They also contain nu-
A.J.C.P. • February 1979
merous bacteria, viruses, and a broad variety of enzymes. A single stool sample can be of any size, but
is often about 250 g of very heterogeneous material.
If this were to contain 5 ml of fully dispersed whole
blood, there would be only about 108 erythrocytes/g
stool, a very small fraction of the total sample. Furthermore, depending at least in part on the site of blood
loss, the erythrocytes could be present intact, as
stroma, or as fragments. Therefore, the feces had to
be fractionated in a fashion designed to recover stroma
and stromal fragments.
A serologic test for human occult blood in human
feces was developed to avoid alleged pitfalls of paperimpregnated guaiac tests. This serologic test consisted
of testing the capacity of a stool fraction to neutralize
appropriately diluted anti-Rh29, the immune response
of a person with Rhnull phenotype. To perform this
test, feces were dispersed in ten volumes of distilled
water, a step that hemolyzed erythrocytes but allowed
for the sedimentation of unwanted large heavy fibers
and particles. Stroma, bacteria, and other small particles were then pelleted by high-speed centrifugation,
resuspended, and mixed with the anti-Rh in the presence of bovine serum albumin. After an hour at 37 C,
pellet solids were again sedimented at high speed, and
supernatant fluid was tested for its residual anti-Rh
activity.
This test consistently identified 108 erythrocytes
added artificially to one gram of Hemoccult-negative
Table 5. Distribution of Positive Tests* for Blood
in Stool Specimens
Day 1
(8
samples)
All four tests
H + HW + C
H + HW + Rh
HW + C + Rh
H + C + Rh
H + HW
H + C
H + Rh
HW + C
HW + Rh
C + Rh
H
HW
C
Rh
None
Total positive tests by
each method
f1 HHW
I Rh
Ic
Day 2
(10
samples)
Day 3
(10
samples)
4
3
0
0
0
0
0
0
1
0
0
0
0
0
0
0
6
2
0
1
0
0
0
0
1
0
0
0
0
0
0
0
0
1
0
1
1
1
0
0
0
0
0
0
0
0
3
3
7
8
4
8
8
10
5
10
3
3
5
3
* Tests: Standard Hemoccult (H), Hemoccult test of feces in water (HW), inhibition
of anti-Rh29 indicative of &]0W erythrocytes/g feces (Rh), radioactivity indicative of
>3 x 107 erythrocytes/g feces (C).
Vol. 71 • No. 2
NONUNIFORM DISTRIBUTION OF OCCULT BLOOD IN FECES
stool, and false-positive results were not encountered.
Theoretically, however, false-negative results could
occur because both proteases and lipases may have
deleterious effects on erythrocytic membranes, particularly with prolonged exposure. In addition,pH values
of less than 5.0 can destroy the Rh antigens of stroma. 10
Similarly, a false-positive result could occur if the final
pellet were to have, for example, a profound enzymatic
effect on the anti-Rh, despite the protection of 2% BSA.
Neither false-positive nor false-negative results were
observed, but the test was evaluated with only several
hundred stool samples.
The Rh serologic test described is not an office procedure. It requires about four hours to compete and
an experienced immunohematology technician to interpret the result. Therefore, the test is not practical unless
warranted by very special considerations. Although
anti-Rh29 was used in these experiments, the more
commonly available anti-Rh 17 (Hr 0 , made by Rh: 1,-17
[-D-] persons) would be almost equally serviceable.
The original reason to construct this serologic test,
namely, false-positive paper-impregnated guaiac tests
for fecal occult blood, seems to have rather minimal
importance. The published frequency of false-positive
results is <2%. 1 1 1 7 In the work now described, little
evidence for false-positive Hemoccult tests was observed, and ingestion of 1 kg of rare beef was unaccompanied by a false-positive standard test result.
However, with a rapid gastrointestinal transit time, it
seems likely that a Hemoccult test of stool could be
falsely positive from ingested meat. False positives
from certain fruits and vegetables 14 do not present a
uniform color for positive.
Dispersal of stool in ten volumes of distilled water
prior to performing a Hemoccult test increases the
working sensitivity for detecting blood by about tenfold. A standard Hemoccult test can detect about 108
erythrocytes/g feces, while a Hemoccult-water test
detects about 107 erythrocytes/g feces. False positivity
due to ingested meat also increases, because the stool
becomes faintly positive by the Hemoccult-water
test after ingestion of 500 g beef.
This study, however, disclosed a far different problem associated with fecal occult blood. Stools are not
homogeneous, and some portions may have evidence
of blood while others do not. It appears that a standard Hemoccult test, while lacking the sensitivity of a
Hemoccult-water test, is quite useful providing the
tiny specimen of stool tested actually contains a representative amount of the blood shed in the gastrointestinal tract by the patient. This implies that a single standard Hemoccult slide may give a false-negative result
just because the wrong portion of stool was tested.
The situation could be improved if a single specimen
209
of stool were tested with either two or more standard
Hemoccult tests on different parts of the specimen
or a Hemoccult-water test of a larger portion. On
days 1 and 2 (Table 5), the Hemoccult-water test was
positive for all samples. These were not positive by
standard Hemoccult test. Unfortunately, the Hemoccult-water test is not as useful for mass screening.
In addition, the intermittent nature of gastrointestinal
bleeding would still necessitate testing on several days.
Acknowledgment:
Dr. Sidney Winawer, Director, Diagnostic
Gastrointestinal Unit, Sloan-Kettering Memorial Hospital and
Associate Professor of Medicine, Cornell University Medical College, New York, advised the authors in the preparation of this report.
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