123
616.34-008.3-074
THE BENZIDINE TEST FOR OCCULT BLOOD IN FAECES 1
B Y C. D. N E E D H A M AND R. G. SIMPSON
(From the Royal Infirmary and Woodend Hospital, Aberdeen)
types of ulcerative lesions of the digestive tract are encountered in
clinical practice, b u t they often elude diagnosis until the disease has progressed
to a late stage. I n some cases clinical evidence may not appear to provide
sufficient grounds t o warrant radiological examination, and in others the suspicion of organic disease is aroused, but radiological studies give negative or
inconclusive results. I n spite of help which may be obtained from further
special investigations, particularly from endoscopic methods, there remain
many cases in which some additional diagnostic aid is desirable. The possibility
t h a t actively progressive lesions of the alimentary tract may betray their
presence by causing small amounts of blood to appear in the stool has been
considered for many years. Leech (1907) stated t h a t Korczynski and Jaworski
(1886) suggested the prussian blue reaction as a chemical test for detecting very
small amounts of blood in faeces, though it appears t h a t Boas (1901) was the
first to use the expression 'occult bleeding', stressing the value of its detection
in the diagnosis of carcinoma of the alimentary tract. Since then various
chemical tests have been suggested and used in clinical practice, the benzidine
a n d guaiac tests being the most popular in this country.
VARIOUS
A practical form of the now commonly used guaiac test had been described
b y Weber (1893), but Adler and Adler (1904) were among the first to employ
the benzidine reaction in testing for occult blood in faeces. This type of benzidine test, which requires a concentrated or saturated solution of benzidine in
glacial acetic acid and hydrogen peroxide, has with minor modifications been
widely used since t h a t time, and is still the one most frequently advocated
(Bell, 1923; Burger, 1934; Marshall, 1938; Murphy, 1939; Johnson and Oliver,
1941; French and Douthwaite, 1945; Harrison, 1947; Hawk, Oser, and Summerson, 1947; Gradwohl, 1948; Lambie and Armytage, 1948; Kolmer, 1949;
Stewart and Dunlop, 1949). Gregersen (1919) realized t h a t the usual form of
the test was too sensitive for clinical use, because the faeces from healthy
people frequently gave a positive result. He clearly demonstrated t h a t the
sensitivity of the test depended on the concentration of benzidine in the test
solution, an 8 per cent, solution detecting 1 : 20,000 and a 0-5 per cent, solution
1 : 500 blood in faeces. He concluded t h a t a powder containing one part
of benzidine to four parts of barium peroxide, made up in 50 per cent,
acetic acid to yield a 0-5 per cent, solution of benzidine, and applied direct to
faeces on a glass slide, provided the most suitable test, because it would detect
1
Received July 4, 1951.
Quarterly Journal of Medicine, New Series XXI, No. 82, April 1952.
K
124
C. D. NEEDHAM AND R. G. SIMPSON
clinically significant amounts of blood b u t would not react to the minimal
amounts of blood present in some normal faeces. This modification of the
benzidine test is described as an additional method by Harrison (1947) and by
Kolmer (1949), and is preferred by some other authors (Aaron, 1924; Ogilvie,
1927; Alvarez and Wight, 1929; Stitt, Clough, and Clough, 1939; Kirschen,
Sorter, and Necheles, 1942; Bockus, 1944; Todd, Sanford, and Stilwell, 1948;
Hutchison and Hunter, 1949).
So many modifications of the benzidine test have been described t h a t there is
obviously a wide divergence of opinion, not only as to the best method of carrying out the test, but as to its clinical application and interpretation. I t appears
t h a t insufficient attention has been directed to the desiderata of a test the function of which is to detect occult blood in faeces. We suggest t h a t t h e essential
requirements of such a test are as follows.
1. I t s sensitivity must be standardized, and must be sufficient to detect
clinically significant .amounts of blood, b u t not so great as to react t o t h e
minute traces of blood t h a t may be present in normal stools.
2. The test should not be affected by taking an ordinary diet or commonly
used medicines. There persists a widespread belief t h a t foodstuffs containing
chlorophyll (Bell, 1923; Aaron, 1924; Rosenthal, 1940; French and Douthwaite,
1945; Gradwohl, 1948; Hutchison and Hunter, 1949; Savill, 1950) and medicines containing iron (Bell, 1923; Burger, 1934; Lambie and Armytage, 1948;
Hutchison and Hunter, 1949; Stewart and Dunlop, 1949; Price, 1950) will give
rise to false positive reactions with the stool benzidine test, although this has
been denied by other authors (Adler, 1921; Abrahams, 1923; Ogilvie, 1927;
Schwartz and Vil, 1947; Todd, Sanford, and Stilwell, 1948). I t is also usually
advised t h a t meat should be excluded from the diet for three or four days
before collecting the faeces for the benzidine test. Although some authors
(Ogilvie, 1927; Alvarez and Wight, 1929; Johnson and Oliver, 1941; Schwartz
and Vil, 1947; and Todd, Sanford, and Stilwell, 1948) have stated t h a t previous
dietary restrictions are not necessary if the Gregersen type of test is used, we
have been unable to find any adequate body of evidence to establish this claim.
I t appears to be true that meat in the diet may often cause a positive result
when tests with a concentrated solution of benzidine are used (White, 1909;
Hektoen, Fantus, and Portis, 1919; Bell, 1923; Bramkamp, 1929; Kiefer, 1934;
Hoerr, Bliss, and Kauffman, 1949), and this is not very surprising, since Abrahams (1923) and Bell (1923) both showed t h a t as little as 1 ml. of blood taken
by mouth could cause a positive stool reaction. The consequent dietary restriction which must be imposed renders the test of very limited value, since it cannot be used in the out-patient department, and even in the wards it is scarcely
practicable as a daily procedure for diagnostic purposes.
3. A minimum of apparatus should be required, and it should be possible to
carry out the test quickly and easily in the test-room of the ward or out-patient
department, using faeces either from a specimen-container or from a rectal
glove-finger smeared on white absorbent paper. Any test which is complicated
or time-consuming will not be done frequently, and so will not be used as a
T H E B E N Z I D I N E TEST FOR OCCULT BLOOD I N FAECES
125
routine either in the out-patient department or on serial specimens from
selected patients in the ward.
4. The test should be reasonably inoffensive and hygienic; a procedure which
involves the transference of a piece of faeces to a test-tube, the addition of
water, and boiling, followed by the pouring of some of the faecal suspension
into another test-tube and its subsequent disposal, is necessarily objectionable.
For several years there has been in general use in the wards of the Aberdeen
Royal Infirmary the modification of the Gregersen (1919) test which is described
in the next section of this paper. This test is a clean and simple procedure
requiring a minimum of equipment, and the present investigation is designed
to decide whether its sensitivity is such t h a t it will detect clinically significant
amounts of blood in faeces, but will avoid giving false positive reactions when
patients are taking ordinary diets or iron-containing medicines.
The Present Investigation
The modified Gregersen benzidine test used throughout the present investigation has been carried out as follows. Individual powders wrapped in wax paper,
each consisting of a finely divided mixture of benzidine hydrochloride 25 mg.
and barium peroxide 200 mg., are dispensed or bought ready prepared. 2 A
powder prepared in this way will retain its potency for more than a year, and
all that is necessary to make up the test solution is to shake up one of the
powders in 5 ml. of glacial acetic acid in a clean test-tube, thus obtaining a 0-5
per cent, solution of benzidine hydrochloride. Then either the examining finger
of a rectal glove or a clean orange-stick dipped in a faecal specimen is smeared
on white filter-paper, and a little of the benzidine solution is poured over the
smear. A blue colour appears if the faeces contain blood. The blue colour may
not be apparent in a dark brown or black faecal smear, but then the white
paper serves as a very efficient background as the blue or blue-green colour
spreads out from the smear into the surrounding white paper. The resulting
colour reactions have been graded and interpreted in the following manner:
Positive ( + ): a deep blue colour, appearing within 15 seconds.
Weakly positive ( ± ) : a greenish-blue colour, appearing within 30 seconds.
Negative (N): no coloration appearing within 30 seconds.
The investigations undertaken in the present study may be grouped under
three main headings: they concern the sensitivity of the test, its selective
properties, and its routine use in the out-patient department.
The sensitivity of the test. 1. Serial dilutions of normal blood in water and in
faeces were tested, and the results are shown in Table I. The aqueous solutions
were poured on to white filter-paper and the test solution added. The procedure
for the faecal dilutions requires further explanation. Three separate specimens
of benzidine-negative stools of medium brown colour and of average consistency
were each weighed out in six exact 0-5 gm. amounts on watch-glasses. I n t o
2
These powders may be bought ready prepared from Messrs. Allen and Hanbury.
C. D. NEEDHAM AND R. G. SIMPSON
126
these portions there was intimately mixed 0-5 ml. of oxalated normal blood in
serial aqueous dilutions, so that for each stool a series of faecal emulsions was
obtained containing 2 per cent. (1: 50), 1 per cent. ( 1 : 100), 0-5 per cent. (1:200),
0-2 per cent. (1:500), 0-1 per cent. (1 : 1,000), and 0-05 per cent. ( 1 : 2,000)
respectively of whole blood. The test was then carried out in the usual manner
TABLE I
The Modified Gregersen Test: Ranges of Sensitivity to Blood in Graded Dilutions
in Water and in Faeces
Nature of
diluent
Tap water
Faeces:
Sample I
Sample II
Sample III
Serial dilutions of blood
,
~
*
^
1 : 50 1 : 100 1 : 200 1 : 500 1 : 1,000 1 : 2,000 1 : 10,000 1 : 50,000 1 : 100,000 1 : 500,000
+
+
+
+
+
+
±
+
..
..
+
N
+
+
..
±
±
N
+ to ±
±
N
N
N
N
on each of the faecal emulsions. The test was found to be sensitive up to approximately 0-2 per cent. (1 : 500) of blood in faeces.
2. After the establishment of the in vitro sensitivity of the test, it was necessary to determine the smallest quantity of blood which must usually be introduced into the stomach in order to produce a positively-reacting stool. Seventeen ward patients were studied in this way, only those subjects being chosen
in whom potential sources of spontaneous bleeding into the ahmentary tract
could be reasonably excluded. I t was found particularly important to inquire
and examine for recent epistaxis, bleeding gums, haemorrhoids, and anal
fissures. In women the dates of menstruation had to be taken into account.
From each of the patients selected for the study a representative sample of
every stool that was passed was saved in a waxed carton, the date and time
being noted on each. All subjects continued their accustomed—usually full—
hospital diets, but were not allowed to have liver or black puddings. 3 Brushing
of the teeth was forbidden, because many hospital patients have easily-bleeding
gums. As soon as consistently negative stools had been obtained for four
consecutive days, a measured quantity of blood, freshly obtained from the
patient's arm and diluted with 5 to 10 ml. of normal saline, was injected into
the stomach through a Ryle's tube which had been swallowed immediately
beforehand. Care was taken to apply only the gentlest aspiration in making
certain t h a t the tube was in the stomach. The blood was followed by a further
10 ml. of normal saline in order to ensure complete emptying of the tube, which
was then withdrawn. No further blood was given until the patient's stool
benzidine reaction had reverted to negative, and had remained so for at least
four days after the previous feeding of blood. The results of this part of the
investigation are shown in Table II. I t was unfortunately not possible to do a
full series of tests on each patient, but the results seem to show t h a t 3 to 5 ml.
of blood is necessary to cause a positive (-f) reaction.
3
Blood constitutes one-third to one-quarter by weight of a black pudding, each
pudding weighing approximately five ounces.
T H E B E N Z I D I N E TEST FOR OCCULT BLOOD I N FAECES
127
The selective properties of the test. The next group of experiments was designed
to show whether there are substances other t h a n blood which, when taken by
mouth, can cause a positive benzidine reaction in the stool. The types of substances investigated were (1) certain medicinal preparations of iron salts, and
(2) a wide variety of common foodstuffs.
TABLE II
Results of Stool Benzidine Tests in 17 Patients after Intragastric
of Measured Quantities of Blood*
Administration
Quantities of blood given by
Ryle's tube
Case
number
1
2
3
4
5
,
1 ml.
N"
N
2 ml.
N
N
N
i
±
±
N
(i
7
8
9
10
11
12
13
14
15
16
17
N
N
N
NT
N
3 ml.
N
N
N
±
N
N
N
+
±
5 ml.
N
10 ml.
15 ml
+
±
+
N
-j-
+
±
±
±
-f+
+
±
+
+
+
* Each symbol in the Table signifies the maximum strength of the stool benzidine
reaction during a period of four days after each separate administration of blood.
1. Using both the modified Gregersen test and the more commonly used type
of benzidine test, we examined the following substances:
A. Iron and ammonium citrate: (i) a standard ward mixture containing
30 grains to the fluid ounce, both with and without the addition of 50 per cent.
v/v of N/10 HC1; (ii) a thick emulsion of blood-free faeces in the standard ward
mixture. No positive result was obtained.
B. Pil. ferrous sulphate, 3 grains: (i) the whole pill crushed; (ii) the green
coating crushed; (hi) the inner portion crushed. No positive result was obtained.
C. Stools containing iron. We examined a series of stool specimens from
each of five subjects, of whom three had been taking iron and ammonium citrate,
60 grains daily, and the other two pil. ferrous sulphate, 9 to 18 grains daily, for
at least 10 days before the experiment began. Although in every instance the
stools were dark-grey or black, a positive benzidine reaction was never obtained.
The muddy discoloration imparted to the benzidine solution in the usual form
of the test should not be mistaken for a true positive colour reaction.
2. Using the modified Gregersen test, we examined the possible effect of
dietary constituents on the stool benzidine reaction.
A. Random samples of various items of hospital food were crushed and
128
C. D. NEEDHAM AND R. G. SIMPSON
rubbed on white filter-papers and tested in the usual manner. The results
obtained were as follows.
(i) Positive ( + ): black pudding, raw or fried; liver, raw or fried; roast mutTABLE
III
Results of Study of 187 Consecutive Out-Patients who had Eaten Meat during
Preceding Three Days
Numbers of patients
f
IV
,
Stool
Potential
No apparent
Not followed
benzidine
*'source of
cause for
to final
test
bleeding
bleeding
diagnosis
Totals
+
49
7f
0
56
±
20
6
0
26
N
18
67
20
105
Totals
87
80
20
187
* Including conditions listed under Group A and Group B, Table IV.
t This number includes four who had eaten black pudding and one other who had eaten
approximately 4 ounces of fried liver.
Negative (N)'105
Total number of
cases '187
No apparent cause
For bleeding
apparent cause tor
bleeding, but positive test
explained on dietary grounds
/
J Potential source of
bleeding present
Not Followed to
final diaqnosis
FIG. 1. Analysis of results of the benzidine test in 187 patients who had
eaten meat. The positive results explained on dietary grounds occurred in
the faeces of four patients who had eaten black pudding and of another who
had eaten approximately four ounces of fried liver.
t o n ; meat stew; rabbit, stewed; chicken, boiled; fish, fried or boiled; tinned
luncheon m e a t ; turnip, raw; potato, raw.
(ii) Weakly positive ( ± ) : green peas, boiled; lettuce, raw; tripe, jellied.
(hi) Negative (N): turnip, boiled and mashed; potato, boiled or roasted;
carrot, raw or boiled; tomato, raw; cabbage, raw or boiled; spinach, tinned;
kale, raw or boiled; onion, raw; meat and vegetable broth; various brands of
meat extract, including oxo and bovril; lemon juice; orange juice; apples, raw
or stewed; prunes, stewed; egg custard; curds and whey; egg white; egg yolk;
milk; cheese; chutney; red-currant jelly; infusion of t e a ; coffee, essence, powder,
or grounds; cocoa powder.
T H E B E N Z I D I N E TEST F O R OCCULT BLOOD I N FAECES
129
B. The above results, together with the fact t h a t the patients in the bloodfeeding experiment were taking normal diet throughout prolonged periods of
daily observation, suggested t h a t foodstuffs other t h a n liver and black pudding,
T A B L E IV
Results of Stool Benzidine Test performed on 603
Out-patients
Number of cases
Stool benzidine result!
Group A:
1. Chronic duodenal ulcer
.
.
.
.
.
2. Chronic gastric ulcer
.
.
.
.
.
.
3. Clinical duodenal ulcer (barium meal X-ra}' negative)
4. Gastric cancer
.
.
.
.
.
.
.
5. Oesophageal (peptic) ulcer or hiatal hernia
6. Oesophageal cancer
.
.
.
.
.
.
7. Pancreatic cancer
.
.
.
.
.
.
8. Non-specific colitis
.
.
.
.
.
.
9. Diverticulitis
.
.
.
.
.
.
.
10. Colonic cancer
.
.
.
.
.
.
.
11. Other organic conditions (including bleeding gums,
haemorrhoids, and anal fissure) .
.
.
.
Total, Group A .
Group B :
1. Hepatic cirrhosis
2. Congestive heart failure
3. Pernicious anaemia
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Total, Group B
Group C:
1. Vague dyspepsia (results of investigations negative)
2. Diseases of liver and bile-passages (excluding hepatic
cirrhosis)
.
.
.
.
.
.
.
Genito-urinary disorders
.
.
.
.
.
Respiratory tract disorders
.
.
.
.
.
Cardiovascular disorders (excluding congestive heart
failure)
.
.
.
.
.
.
.
.
Neurological d i s o r d e r s . . . . . .
Locomotor disorders
.
.
.
.
.
.
Anxiety neuroses and psychoneuroses .
9. Unclassified sundry conditions
Total, Group C .
Totals
+
±
N
151
24
62
20
6
1
1
8
7
1
64
10
16
10
4
1
22
2
5
5
2
65
12
41
5
27
1
2
2
1
4
11
6
10
308
123
47
138
4
19
5
3
3
2
4
1
12
3
5
1
1
28
16
44
43
11
13
34
1
1
1
10
12
33
11
20
46
21
67
3
1
12
7
11
19
43
20
48
267
*18
10
239
1
Grand Total
603
149 61 393
* This figure includes six patients who had eaten black pudding, and one other who had
eaten approximately four ounces of fried liver.
when eaten in customary quantities, were unlikely to exert a significant effect
on the stool benzidine reaction. We therefore fed five ward patients with
measured quantities of liver and of black pudding, applying the same rigid
precautions as in the blood-feeding experiments. A positive ( + ) reaction was
obtained from the stools of all five patients after t h e y had eaten two black
puddings, one black pudding, eight ounces, five ounces, and three ounces of
fried liver respectively.
130
C. D. NEEDHAM AND R, G. SIMPSON
C. A random series of patients attending the medical out-patient department
were asked whether they had eaten any meat in the previous three days. The
stool benzidine results of the 187 who had eaten meat were recorded, and all
except 20 of the patients were followed to final diagnosis. The results are
summarized in Table I I I and in Fig. 1. In only 13 of the 187 patients was a
positive reaction of any degree obtained in the absence of a proved source of
Negative (i\l)^3,31
Total number of
cases - 603
No apparent
. for bleeding
cause
3 Wo apparent cause For
\ bleeding, but positive test
explained on dietary grounds
Positive M = 149
U ~7~\ Potential source of
I /
I bleeding present
FIG. 2. Analysis of results of the benzidine test in 603 patients. The positive
results explained on dietary grounds occurred in the faeces of six patients who
had eaten black pudding and of another who had eaten approximately four
ounces of fried liver.
bleeding. Of these 13 subjects, five out of the seven who gave a positive (-}-)
reaction had eaten black pudding or liver the previous day.
The routine use of the test in the out-patient department. In order to evaluate
the usefulness and limitations of the modified Gregersen test for occult blood in
clinical practice, we have analysed the medical records of 603 out-patients
whose stools we have tested during the past two years. I n every instance the
faecal smear was made direct from the gloved finger used in the rectal examination, and was tested immediately by the method we have described. The stool
benzidine results together with the final diagnoses are set out in Table IV and
Fig. 2. For the sake both of clarity and of economy of space we have classified
diagnoses under system groups. The results show t h a t a high proportion of
positive (-|-) results was explained by the presence of alimentary tract lesions.
Of the remaining 26 positive ( + ) results seven could be explained on dietary
grounds, and eight others were found in the stools of patients suffering from
the conditions hsted in Group B (Table IV) which appear to be liable to cause
alimentary bleeding. Thus of 603 stool examinations 149 gave positive ( + )
results, and of these only 11 (one in every 13 or 14) appeared to have no clinical
significance.
T H E B E N Z I D I N E TEST FOR OCCULT BLOOD I N FAECES
131
Discussion
The modified Gregersen test used in this investigation is a simple procedure,
not requiring special laboratory facilities. The use of white filter-paper for the
faecal smear has a double advantage over mixing on a glass slide in that the
colour change spreading into the white background is very easily seen and, the
paper being expendable, there is no risk of faecal contamination in its disposal.
Whether glacial acetic acid or 50 per cent, acetic acid is used probably makes
very little difference. I t is not, however, as a convenient second best t h a t we
advocate the modified Gregersen test, but as a method superior to the more
usual form of the benzidine test by reason of its standardized concentration of
benzidine, nicely balanced sensitivity, ready availability, and cleanliness. Much
of the confusion still evident in current literature concerning the necessity or
otherwise of dietary restriction prior to testing the faeces is due to the still
prevalent use of the more usual and over-sensitive type of benzidine test. Even
with this method it is difficult to see how a positive faecal reaction could be
caused by the ingestion of chlorophyll-containing foods or of medicines containing iron salts, since these substances do not yield a positive result even
when subjected to direct testing. We believe that the amount of meat taken in
the ordinary diet will seldom cause false positive reactions when the modified
Gregersen test is used, because (1) the patients used for studying the effect of
feeding varying amounts of blood were given ordinary ward diet throughout
the period of the tests, but their faeces gave consistently negative results until
blood had been administered; (2) we found it necessary to feed patients with
rather large amounts of meat rich in blood (liver and black pudding) before the
faeces gave a positive reaction; (3) the evidence from the out-patient series as
a whole (Table IV) and in particular from the 187 cases in which the previous
diet was reviewed in detail (Table I I I ) suggests t h a t eating meat seldom
accounted for a positive reaction. The next question t h a t arises is whether this
modified Gregersen test is sufficiently sensitive to detect clinically significant
alimentary bleeding. Our findings regarding the in vitro sensitivity of the
modified Gregersen test (Table I) are in substantial agreement with those of
Gregersen himself (1919), who considered it to be sensitive enough for clinical
use. Other observers (Abrahams, 1923; Bell, 1923) have shown that the usual
form of the benzidine test becomes positive after feeding 0-5 to 1 ml. of blood,
b u t we found, using the modified Gregersen test, t h a t at least 3 ml. of blood
was needed to produce a positive reaction (Table II). I n spite of this lesser
degree of sensitivity of the modified Gregersen test, the results with outpatients, listed in Table IV, suggest that it is sensitive enough to detect clinically significant bleeding in most instances where it is occurring. Furthermore,
experience with routine daily testing in the wards has shown that, when
each patient's results are considered as a series, the test is more informative
than when used on a single stool specimen, because one is not misled by the
occasional positive result in an otherwise negative series, or vice versa. Repeated
stool tests—or stool series—are practicable only when a simple form of benzidine
test is used.
132
C. D. NEEDHAM AND R. G. SIMPSON
We do not wish to suggest that this is an infallible screening test for organic
disease of the alimentary tract. Even ulcerating lesions may bleed only intermittently, and it is probable that blood arising from a lesion, particularly in
the more proximal alimentary tract, may be sufficiently altered before it
reaches the stool to render it incapable of giving a positive benzidine reaction.
That destruction of blood does occur in its passage through the gastro-intestinal
tract is suggested by the work of Andrews and Oliver-Gonzalez (1942) who fed
approximately two ounces of calf blood to each of four subjects, and found by
a quantitative method that only 30 to 85 per cent, of the blood was passed in
the faeces. This fact, coupled with the relative insensitivity of the test for
blood diluted in faeces as opposed to water (Table I), probably explains why
we had to feed rather large amounts of blood in order to obtain a positive
benzidine reaction in the stool (Table II). The single examination possible in
the out-patient department inevitably gives some positive results which remain
unexplained after fuller investigation (one in every 13 or 14 in our series).
This error is largely excluded in in-patient studies by repeated tests, b u t it
appears that the routine use of the test in out-patient practice will, with the
minimum of labour and expense, give considerable help in the diagnosis of
gastro-intestinal disorders, provided that one takes care to exclude the presence
of bleeding from the nose, the gums, haemorrhoids, anal fissure, and menstruation. I t is concluded that the modified Gregersen test can give useful information in out-patient as well as in-patient work if interpreted in conjunction with
all the other available evidence.
A cknowledgement
We should like to thank the nursing staff for their willing co-operation in the
in-patient studies.
Summary
1. The literature relating to the development of the benzidine test is briefly
reviewed.
2. The desirable properties of a test for small quantities of blood in faeces
are considered.
3. Some of the limitations of the benzidine reaction as usually employed are
discussed.
4. A modification of the Gregersen type of stool benzidine test is described.
5. In vitro experiments and clinical investigations designed to explore the
suitability of this test for clinical use are described.
6. I t is concluded that this modification of the benzidine test offers significant
advantages over other forms of the test, and will yield useful information when
used in either out-patient or in-patient practice.
REFERENCES
Aaron, C. D. (1924) J. Amer. Med. Ass. 83, 741.
Abrahams, A. (1923) Guy's Hosp. Rep. 73, 137.
Adler, E. (1921) Arch. Verdauungskr. 27, 153.
THE BENZIDINE TEST FOR OCCULT BLOOD IN FAECES
133
Adlcr, O., and Adler, R. (1904) Zts. physiol. Chem. 41, 59.
Alvarez, R. S., and Wight, T. H. T. (1929) U.S. Vet. Bur. Med. Bull. 5, 888.
Andrews, J. S., and Oliver-Gonzalez, J. (1942) J. Lab. Clin. Med. 27, 1212.
Bell, J. R. (1923) Guy's Hosp. Rep. 73, 20.
Boas, I. (1901) Dtsch. med. Woch. 27, 315.
Bookus, H. L. (1944) Castroenterology, Philad., vol. ii, 472.
Bramkamp, R. G. (1929) J. Lab. Clin. Med. 14, 1087.
Burger, G. N. (1934) Guy's Hosp. Rep. 84, 112.
French, H., and Douthwaite, A. H. (1945) An Index of Differential Diagnosis, 6th ed.,
Bristol, p . 117.
Gradwohl, R. B. H. (1948) Clinical Laboratory Methods and Diagnosis, 4th ed., London,
vol. i, 1125.
Gregersen, J . P . (1919) Arch. Verdauungskr. 2 5 , 169.
Harrison, G. A. (1947) Chemical Methods in Clinical Medicine, 3rd ed., London, pp. 498,
502.
Hawk, P . B., Oser, B. L., and Summerson, W. H. (1947) Practical Physiological Chemistry,
12th ed., London, p. 404.
Hektoen, L., Fantus, B., and Portis, S. A. (1919) J. Inf. Dis. 24, 482.
Hoerr, S. O., Bliss, W. R., and Kauffman, J. (1949) J. Amer. Med. Ass. 141, 1213.
Hutchison, R., and Hunter, D. (1949) Clinical Methods, 12th ed., London, p. 69.
Johnson, A. S., and Oliver, E. B. (1941) J. Lab. Clin. Med. 26, 727.
Kiefer, E. D. (1934) Amer. J. Surg. 25, 530.
Kirschen, M., Sorter, H., and Necheles, H. (1942) Amer. J. Digest. Dis. 9, 154.
Kohner, J. A. (1949) Clinical Diagnosis by Laboratory Examinations, 2nd ed., New York,
pp. 265, 1056.
Korczynski, E., and Jaworski, W. (1886) Dtsch. med. Woch. 12, 829 (cited by Leech, 1907).
Lambie, C. G., and Armytage, J. E. (1948) Clinical Diagnostic Methods, Sydney, vol. ii, 848.
Leech, E. B. (1907) Med. Chronicle, 46, 281, 349.
Marshall, C. J. (1938) Chronic Diseases of the Abdomen, London, pp. 40, 97.
Murphy, W. P . (1939) Anemia in Practice, Philad., p. 305.
Ogilvie, A. G. (1927) Brit. Med. J. 1, 755.
Price, F . (1950) Textbook of the Practice of Medicine, 8th ed., London, p . 690.
Rosenthal, E. (1940) Diseases of the Digestive System, London, pp. 39, 98.
Savill's System of Clinical Medicine, ed. Warner, 13th ed., 1950, London, p. 370.
Schwartz, S. O., and Vil, C. S. (1947) J. Lab. Clin. Med. 32, 181.
Stewart, C. P., and Dunlop, D. M. (1949) Clinical Chemistry in Practical Medicine, 3rd ed.,
Edinb., p . 307.
Stitt, E. R., Clough, P.W.,and Clough, M. C. (1939) Practical Bacteriology, Haematology and
Animal Parasitology, 9th ed., London, p. 747.
Todd, J. C , Sanford, A. H., and Stilwell, G. G. (1948) Clinical Diagnosis by Laboratory
Methods, 11th ed., Philad., p . 484.
Weber, H. (1893) Berl. klin. Woch. 30, 441.
White, F . W. (1909) Boston Med. Surg. J. 160, 733.