Porphyrins Coproporphyrins < 200 μg/24 h
Protoporphyrins < 1500 μg/24 h
Bile Negative in adults, positive in children
Trypsin Positive in small amounts in adults, in
greater amounts in normal children
TABLE 7.2: Inspection of feces
Constipation (irritable colon syndrome,
Spastic bowel or rectal narrowing or
Clay colored Obstructive jaundice or presence of Barium
Reddish stool Blood from lower gastrointestinal tract,
Black, tarry stool Bleeding from upper GIT, Iron, bismuth or
Green stool Ingestion of spinach, etc. calomel, presence of biliverdin, seen in patients taking
Parasites Parasitic infestation (discussed later)
fat intake or barium used in X-ray examination.
f. Red color may be due to a diet high in beet or use
g. Drug-induced color changes are given below:
• Black—iron salts, bismuth salts, charcoal
• Green—mercurous chloride, indomethacin,
• Brown staining—anthraquinones
• Red—phenolphthalein, pyrvinium pamoate,
• Whitish discoloration—antacids
• Pink to red to black—anticoagulants (excessive
dose) salicylates causing internal bleeding.
Patients with chronic ulcerative colitis and chronic
bacillary dysentery frequently pass large quantities of pus
with the stool that has to be examined microscopically.
It may also occur in localized abscesses or fistulas
communicating with sigmoid rectum or anus. Large
amounts of pus never accompany amebic colitis. No
inflammatory exudate is seen in the watery stools of
patients with viral gastroenteritis.
Even in slightest quantity is abnormal (Table 7.3).
Characteristic odor varies with the pH of stool; normal pH
is neutral or weakly alkaline.
The pH is dependent on bacterial fermentation and
putrefaction in the bowel. Substances called indole and
Carbohydrate fermentation changes pH to acidic. Protein
breakdown changes the pH to alkaline.
Blood in stools should never be ignored, however, slight
the quantity may be. Bleeding in the upper GIT may give
black-tarry appearance to stools while that arising from
lower GIT may give red color or be seen as frank blood.
¾ Peptic ulcer—gastric or duodenal
¾ Inflammatory bowel disease (Crohn’s disease,
Associated with increased GIT blood loss:
TABLE 7.3: Mucus in stool—causes
Spastic constipation or mucous
colitis. In emotionally disturbed
Neoplasm, inflammation of rectal
Mucus with pus and blood Ulcerative colitis, bacillary dysentery,
ulcerating carcinoma of the colon,
and more rarely, acute diverticulitis or
Villous adenoma of the colon (may
Loss of more than 50–75 mL of blood from the upper
GIT generally imparts a dark red to black color and a tarry
consistency to the stool. Persistence of tarry appearance
for 2 or 3 days suggests loss of at least 1000 mL of blood.
Smaller increases in blood content may not alter
appearance of the stool. Such stools are said to contain
“Occult blood” (usually associated with GIT neoplasm).
Drugs such as salicylates, steroids, indomethacin,
colchicine, iron (used in massive therapy), and
Rauwolfia derivatives are associated with increased
gastrointestinal bleeding in normal persons and with
even more pronounced bleeding when disease is present.
Gastrointestinal bleeding tests may be falsely positive in
the undermentioned circumstances:
¾ Meat in diet contains hemoglobin and enzymes that
can give false positive tests for up to 4 days after eating.
The guaiac method does not require meat-free diet due
¾ Vitamin C taken in quantities greater than 500 mg per
day may cause false negative test for occult blood in
¾ Drugs that may cause a false positive test for occult
¾ Testing method must be followed exactly or the results
¾ Use an aliquot from center of formed stool
¾ Liquid stools may cause false negatives with filter paper
These tests are based upon a little understood chemical
reaction in which the reagent is oxidized by hydrogen
peroxide at low pH (acid added) and catalyzed by the
presence of heme—the intact iron containing porphyrin
All iron heme derivatives are active. Free iron and
free porphyrin rings are not active. The most important
substance, which contains the active ‘heme’ besides
hemoglobin, is myoglobin contained in muscle fibers.
The ideal test for screening should be sensitive enough
to react to a significant amount of blood without reacting
to the minute amounts of blood present in the feces
with substances in diet or in common medicines and at
the same time be simple, easy, rapid and inexpensive to
Benzidine test is an extremely sensitive test and can give
false positives in people on abundant meat diet. Only 1–2%
people with significant bleeding will show a negative test
(false negative). False positives may be overcome in some
cases by boiling the emulsion of feces for 1–2 minutes and
Benzidine reagent consists of 4 g benzidine base/100 mL of
glacial acetic acid. It is stable for about 4 months. Emulsify
peasized bit of feces in 5 mL of water. Mix 1 mL emulsion
and 1 mL of reagent in test tube and add several drops of
3% H2O2. Positive reaction is indicated by the appearance
of a blue color in the mixture and is reported as follows:
Trace —Faint blue color after 1 minute
1+ —Definite blue-green slowly
This is less sensitive. Has 5% false positive in patients on
nonvegetarian diet and 3–5% false negatives. It is a better
screening test. With loss of 20–30 mL of blood, all tests will
Guaiac reagent consists of 1 g guaiac in 5 mL of 95% ethanol
(stable in brown bottle for a month in a refrigerator).
To an emulsion of feces—or better yet, a small smear of
feces on a piece of filter paper add 2–3 drops of gum guaiac
solution, 2–3 drops of glacial acetic acid and 2–3 drops of
Positive tests are reported as:
Trace — Faint blue-green in 1 minute
3+ — Deep blue almost immediately
116 Concise Book of Medical Laboratory Technology: Methods and Interpretations Orthotolidine
This test has an intermediate sensitivity and is replacing
other tests, though, not in India.
Mix: Orthotolidine barium peroxide 200 mg. Glacial acetic
acid 5 mL (Stable only for one day).
¾ Using a clean applicator stick, smear the stool on a
¾ Pipette a few drops of the reagent on to the filter paper
¾ After exactly 30 seconds, examine for a blue color.
A blue green color appearing within 30 seconds means a
Fecal occult blood is a term used to describe the presence
of blood in the feces. Blood is present in the feces due to
bleeding from the gastrointestinal tract. Small increases
in blood content may not alter the appearance of the
stool and such stools are said to contain “occult blood”,
detection of which can be most useful in uncovering and
localizing disease. Hemoglobin levels of 5 mg/dL or more
are diagnostically significant.
Screening for occult blood is especially important
because over one half of all cancers (excluding skin) are
those of the gastrointestinal tract. Early diagnosis and
treatment of patients with colonic cancer results in a
relative good prognosis for survival.
Hemospot test is useful in the detection of bleeding
caused by gastrointestinal disorders such as colitis, polyps,
diverticulitis, colorectal cancer and hookworm infestation.
Fecal occult blood tests are recommended for use in:
1. As an aid to routine physical examinations.
3. Screening for gastrointestinal bleeding from any
source including colorectal cancer.
1. Hemospot test cards consisting of a filter paper
impregnated with the guaiac resin (reactive surface).
2. Developer solution consists of stabilized hydrogen
peroxide solution, which is ready to use.
Store the reagent at 20–30°C, in a cool place away from
direct sunlight, fluorescent light, UV rays and moisture. Do
The shelf life of the reagents and test cards is mentioned
on the kit/developer solution label.
If blood is present in the stool sample, the hematin in the
hemoglobin molecule catalyzes the release of oxygen from
the hydrogen peroxide, which in turn oxidizes the colorless
phenolic components of gum guaiac to colored quinones.
During test, after the addition of the developer solution
to the reactive surfaces of the result window, the reaction
area turns blue if occult blood is present in the sample. If
the reaction area does not change color, then it indicates
that there is no occult blood present in the sample.
1. In vitro diagnostic reagent for laboratory or professional
use only. Not for medicinal use.
2. The kit contains hydrogen peroxide solution, which
may be irritating. Avoid contact with eyes, skin and
clothing. In case of contact, flush with large quantities
3. Do not expose the test cards and developer solution
to direct sunlight, fluorescent light and UV rays.
Positive control provided with the kit should be run
occasionally to validate the performance of the test cards
Preparation and Sample Collection
1. As for all occult blood tests, certain medications such
as aspirin, indomethacin, phenylbutazone, reserpine,
corticosteroids and nonsteroidal anti-inflammatory
drugs can induce gastrointestinal bleeding and cause
false positive results. These medications should be
temporarily discontinued with the consent of the
physician for 7 days prior to testing and during the test
2. Vitamin C when taken in amounts greater than 250
mg per day has been shown to induce false negative
results. Rectal medications (suppositories) and iron
containing medications may also interfere with
these tests and should be discontinued 2 days before
and during the test period with the consent of the
3. For at least 2 days before and during the test period,
all raw meat and red meat should be avoided. Raw
broccoli, cauliflower, radishes and turnips may cause
false positive results, hence should be avoided.
1. A clean dry detergent free glass or plastic container of
a suitable size is ideal for collection of the specimen.
Urine should not be passed simultaneously into
the collection container. Clean pieces of plastic are
convenient for transferring stool from the collection
container to the transport vessel.
2. The stool samples should be collected from different
areas of the formed stool (samples from the outside
of stool are most likely to reflect the condition of the
lower colon, while specimens taken from inside of
the stool are more likely to reflect conditions of the
upper gastrointestinal tract) and also provides a more
representative sample to be tested.
3. The two test fields provided in Hemospot facilitate
detection and localizing the source of bleeding.
Because bleeding may be intermittent, it is preferable
to collect specimens from different bowel movements,
Material Provided with the Kit
2. Dropper bottle containing developer solution
Gloves, stopwatch, rust free needle/pin.
No comments:
Post a Comment
اكتب تعليق حول الموضوع