EXERCISE NO. 4 ROUTINE STOOL EXAMINATION Flashcards
The presence of intestinal parasites is primarily identified through the direct examination of stool. Morphological diagnosis of parasites consists of two steps:
(1) detection of the parasite or its parts in clinical samples
(2) its identification
depends on collection of the appropriate specimens, and their recovery and examination by suitable techniques.
Detection
requires adequate skill and expertise in recognizing the parasite in its various stages and its differentiation from morphologically similar artifacts.
Identification
Once a stool specimen has been received in the laboratory, the (?) of laboratory testing, also referred to processing, begins.
analytic phase
In this phase, processing and examination of stool specimen is conveniently divided into the following parts:
- Macroscopic or physical examination
- Chemical examination
- Microscopic examination
Stool specimens are submitted to the laboratory either in the (?) or as (?) .
fresh state
preserved samples
If the stool specimen is fresh and unpreserved, as soon as it is received in the laboratory, (?) must be checked.
the color and the consistency
The first indication of gastrointestinal disturbances can be often provided by the changes in the (?) and (?) of the normal stool.
However, this step is skipped if stool specimen is already in (?).
brown color
formed consistency
fixative
Laboratories that receive the stool specimen in (?) must rely on information that is submitted with the specimen as to the color and consistency of the specimen.
preservative vials
The normal light to dark brown color of stool is due to stercobilin which is formed from intestinal oxidation of (?).
stercobilinogen
The (?) is important because It is worth noting that it may be pathologic or physiologic changes.
color of a stool
Color variations and associated conditions include the following:
bright red
black/tarry
white, gray, clay / putty (acholic)
green, or blue
upper GIT bleeding, beets, tomatoes, food coloring
•bright red
upper GIT bleeding, iron therapy, antidiarrheal compounds (charcoal, bismuth)
•black/tarry
•white, gray, clay / putty (acholic)
bile duct obstruction
barium sulfate used in x-ray exams
excess fats (steatorrhea)
milk
green vegetables oral antibiotics - owing to oxidation of bilirubin to beliverdin,
•green, or blue
Different types of stool specimen according to consistency are:
•formed
•semi-formed
•soft
•liquid ( or watery)
The (?) in a stool specimen may serve as an indication of the types of potential parasites present.
consistency or degree of moisture
are generally observed in soft or liquid specimen.
Protozoan trophozoites
This is the rationale for the time limit recommendation for examination (?) of watery stool.
within 30 minutes of collection
are often found in formed or semi-formed specimens.
Cysts
may be found in any type of stool specimen
Helminth eggs and larvae
the chances of finding helminth eggs and larvae in liquid stool are reduced by the
dilution factor
(?) in the specimen may have parasitic indications.
Macroscopic abnormalities
Examine the surface (top and bottom) of the stool specimen and broken up the with applicator sticks to check for parasites (e.g., tapeworm proglottids or, less commonly, adult pinworms).
• Adult worms.
Samples containing adult worms may be carefully washed through a
wire screen
This process allows for the retrieval and examination of the parasites for identification purposes.
Wire screen
• Blood and/or mucus in loose or liquid stool may suggest the presence of (?) in the large intestine.
amoebic ulcerations
Some of this material should be preferentially examined microscopically for (?). Although if present, neither one necessarily indicates a parasitic infection.
trophozoites
is the frequently performed chemical test on stool specimens.
Fecal occult blood testing (FOBT)
It was originally used primarily to test suspected cases of gastrointestinal diseases, which may or may not be related to parasitic infection.
Fecal occult blood testing (FOBT)
it has currently become widely used as screening procedure for the detection of colorectal cancer
Fecal occult blood testing (FOBT)
though it is not intended to replace other diagnostic procedures such as proctosigmoidoscopy, barium enema or x-ray studies)
Fecal occult blood testing (FOBT)
may produce color changes in the stool, from bright to dark red to black depending on the area of the intestinal tract from which the bleeding is occurring.
bleeding in the GIT
no visible signs of bleeding may be present in a (?) in the stool
small amount of blood
Bleeding in excess (?) of stool is considered pathologically significant
2.5 ml / 150 g
is defined as a very small amount of blood that is not visible to the naked eye and is detected by chemical means only
Occult blood
General Principle: Occult blood testing is based on the (?) of hemoglobin decomposing (?) into water and oxygen. The liberated oxygen oxidizes a (?) into a colored product.
pseudoperoxidase activity
hydrogen peroxide
colorless chromogen
The chromogens, in order of decreasing sensitivity
benzidine, o-toluidine, and guaiac
is preferred for FOBT because it would detect clinically significant amounts of blood but would not react to the minimal amounts of blood present in some normal stool.
Guaiac
Example of commercial test kit
e.g, HemaScreen Lab Pack
• Patients should be instructed to avoid eating the following for 3 days prior to specimen collection to prevent false-positive results due to the presence of dietary pseudoperoxidase in stool:
red meats, rare meats
horseradish, melons and cantaloupe, raw broccoli, cauliflower, turnips
should not be taken for 7 days prior to specimen collection to prevent possible gastrointestinal irritation that may cause false- positives.
Aspirin and other NSAIDs, and heavy alcohol consumption
• Vitamin C (in excess of 250 mg / day) and other iron supplements containing Vitamin C should be avoided for
2 days prior to specimen collection
• Other causes of false-positives:
menstrual and hemorrhoid contamination
is a strong reducing agent that will interfere with the peroxidase reaction (false-negative).
ascorbic acid
Vitamin C (in excess)
250 mg / day
– source of myoglobin and hemoglobin
red meats, rare meats
Which of the following characteristics is NOT observed during the macroscopic examination of stool specimens?
D. Occult blood
What is the color of a tarry stool?
C. Black
Protozoan cysts are generally observed in:
C. formed stool
The preferred chromogen when testing for occult blood in stool is:
D. guaiac
Which of these procedures is involved in the microscopic examination of stool specimens for parasites?
C. Performing a wet mount
Amoeba trophozoite motility is best observed using:
C. unstained saline wet mount
The microscopic examination of a stool specimen is performed to detect ova and parasites, thus it is normally called the
Ova and Parasite (O & P) Examination
refers to the egg stage of select parasites and parasites encompass the other morphologic forms that may be present.
ova
Routine stool O & P examination consists of the following distinct techniques. Each of these methods is designed for a particular purpose and forms an integral part of the total examination.
direct fecal smear (DFS), and Kato thick smear (KTS)
is prepared by using an applicator stick to mix a small amount (about 2 mg) of unfixed stool in normal saline solution (NSS) and in Iodine solution, known, respectively, as (?) wet mounts.
DIRECT FECAL SMEAR
saline (unstained) and iodine (stained)
Normal saline solution
Sodium chloride (NaCl) ………………………………………………. Distilled water…………………………………………………………… 0.85 gms 100 ml
- Dissolve the sodium chloride in distilled water in a flask.
- Transfer into clean, clear glass stoppered or screw-capped bottle.
- Label as NORMAL SALINE SOLUTION (or 0.85% NaCl) with an expiration date of 1 year.
- Sterilize by autoclaving at 121 oC for 15 min.
- Store at room temperature.
Normal saline solution
Lugol’s iodine (stock, 5% solution)
Iodine crystals…………………………………………………………. Potassium iodide……………………………………………………… Distilled water………………………………………………………….. 5 gms 10 gms 100 ml
- Grind the dry iodine and potassium iodide in a mortar. 2. Dissolve the potassium iodide and iodine crystals in distilled water in a flask. 3. Store in a amber, glass-stoppered or screw-capped bottle at room temperature. Some excess crystals of iodine should remain on the bottom of the bottle. 4. Label as LUGOL’S IODINE (STOCK, 5%) with an expiration date of 1 year. (The stock solution remains good as long as an excess of iodine crystals remains on the bottom of the bottle)
Lugol’s iodine (stock, 5% solution)
- an alternative for Lugol’s iodine solution
D’Antoni’s iodine solution
D’Antoni’s iodine solution
Potassium iodide (KI) …………………………………………… 1.0 gms Iodine crystals ……………………………………………………… Distilled water …………………………………………………….. 1.5 gms 100 ml
- Grind the dry iodine and potassium iodide in a mortar. 2. Dissolve the potassium iodide and iodine crystals in distilled water in a flask. 3. Store in a amber, glass-stoppered or screw-capped bottle at room temperature. Some excess crystals of iodine should remain on the bottom of the bottle. 4. Label as D’ANTONI’S IODINE SOLUTION with an expiration date of 1 year. (The stock solution remains good as long as an excess of iodine crystals remains on the bottom of the bottle) The solution is ready for immediate use. Aliquot some of the iodine into a brown dropper bottle. The working solution should resemble strong tea and should be discarded when it lightens in color (usually within 10 to 14 days).
D’Antoni’s iodine solution
is the simplest and most commonly utilized method of examination and employed to demonstrate all morphologic forms of parasite in stool: protozoan trophozoites and cysts, and helminthic eggs and larvae.
DFS (saline and iodine wet mount)
Other formed structures, such as RBCs and WBCs can be seen when examining a
wet mount
Because the amount of stool used in (?) is very small, light infections may not be detected.
DFS
If the specimen is received in the laboratory in a (?), this procedure can be eliminated from the O&P examination, and time must be better spent on concentration techniques
fixative
are particularly useful for detecting motile trophozoites (e.g. Entamoeba histolytica, Balantidium coli and Giardia lamblia.)
Saline mounts
Motile rhabditiform larvae of (?) are also readily detected in freshly passed stool. Chromatoidal bars in some protozoan cysts are also demonstrated as refractile bodies.
Strongyloides stercoralis
(?), because it is a contrast dye, enhances the detail of protozoan cysts. The cytoplasm will stain (?), the nucleus will be (?), and the glycogen will be deep brown. Helminth eggs and larvae can also be detected using this preparation.
Iodine
golden yellow
pale and refractile
kills and distorts any trophozoites present and render parasites nonmotile.
iodine
is a method introduced by by Kato and Miura in 1954.
Kato thick smear
About 50 mg stool (the size of two monggo beans) is placed on a slide and covered with a wettable cellophane strip soaked in glycerol-malachite green solution. This is also known as the
cellophane-covered thick smear
Glycerol-malachite green solution
Glycerol (glycerine)……………………………………………………… 3% aqueous malachite green………………………………………. Distilled water……………………………………………………………….. 100 ml 1 ml 100 ml
(?) is the clearing solution, while (?) – gives color to the cellophane, giving a pale green background to minimize the brightness of the microscopic field therefore prevent eye strain and fatigue.
Glycerol
malachite green
(?), cut at least 22 x 30 mm, is soaked in glycerol-malachite green solution for at least 24 hours prior to use. Note: (?) is often used, and the malachite green may be omitted in the preparation.
Cellophane strip
Green cellophane
The preparation is left for about 20-30 minutes at room temperature before microscopic examination. During this time, the (?) clears the stool, enabling the helminth eggs to be seen distinctly under low-power magnification.
glycerol
•The slide is examined within 1 hour after preparation. Allowing the slides to stand for a long period of time will cause drying and thin shells of hookworm egg will become (?) and will be difficult to see.
too transparent
is simple and economical, and is therefore useful in mass survey of stool for intestinal helminth eggs, including Schistosoma species.
KTS
It is very good in detecting eggs with thick shells (e.g., Ascaris and Trichuris) but not eggs with thin shells (e.g., hookworm).
KTS
Usefulness is limited if stools are diarrheic or watery. This method is not useful for diagnosis of protozoa or helminth larvae.
KTS
Stool normally consists of (?) such as bacteria and yeast.
food residues, various digestion products, sloughed epithelial cells and microorganisms
refer to other things, living or non-living, present in stool that are not parasites but resembling parasitic trophozoites, cysts, eggs, larvae, and adult worms, which could mislead laboratory worker in identifying them as parasites.
Artifacts
Many such artifacts arise from the large array of (?)ingested every day by humans.
vegetable and meat products
Cells of human (?) origin may also mimic pathogenic or commensal protozoa in their appearance.
enteric
(?) with human or nonhuman parasites are known to occur following ingestion of contaminated or infected meats.
Spurious infections
The use of (?) offers another mechanism by which specimens are contaminated with extraneous organisms.
improper collection techniques
Laboratorians must be able to differentiate (?) present in a specimen from actual parasites. Therefore, it is important to become familiar with these artifacts.
extraneous materials
