Beneficial for students

1. STOOL EXAMINATION
10/29/2021 1
Analysis of Stool Examination

2. INTRODUCTION
Examination of sample of stool is easily done
Useful in the evaluation of diarrheal diseases,
parasitic infestations, colorectal carcinoma
and malabsorption.
10/29/2021 2
Analysis of Stool Examination

3. COLLECTION
CONTAINER: Stool sample is collected either in a
wide mouthed glass or plastic jars with a screw
cap
Container should be clean and dry
METHOD OF COLLECTION: Sample is transferred
from a clean bed pan or toilet into the container
AMOUNT OF SAMPLE: Stool required is small and
about 2 -5g of the stool sample is adequate
10/29/2021 3
Analysis of Stool Examination

4. PRCECAUTIONS IN COLLECTION
Morning sample is preferred
Sample should be labeled and the time of collection to
be mentioned
Contamination with either urine or other substances in
the bed pan or toilet should be avoided
Stool must be fresh
Examine within 1 hour of collection
If blood/mucus/any other abnormal gross features are
present in the stool, it should be included in the
sample collected
10/29/2021 4
Analysis of Stool Examination

5. PRESERVATION
Formal –saline can be used as preservative
which preserves morphology of protozoa and
helminthic eggs
10/29/2021 5
Analysis of Stool Examination

6. STOOL EXAMINATION
PHYSICAL EXAMINATION
QUANTITY : The quantity of stool varies from 100-
250g/day depending on the type of diet consumed
CONSISTENCY AND FORM:
Normal feces is well –formed
Extensively hard stool is observed during constipation
Large bulky, frothy, pale, foul smelling stool which
floats on water is characteristic of steatorrhea (Poor fat
digestion )
Rice water stool- cholera
Watery/semisolid –diarrhea, dysentry
10/29/2021 6
Analysis of Stool Examination

7. COLOR :
Normal – Golden brown – stercobilin(Pigment
derived from bilirubin metabolism)
Black tarry stool – Usually due to altered blood in
stool –melena
Source of blood – Bleeding from the upper
gastrointestinal tract
Black tarry stool – observed in iron administration
Bright red color: Due to bleeding from the lower
GIT like bleeding piles
Clay colored stools: observed in obstructive
jaundice
10/29/2021 7
Analysis of Stool Examination

8. ODOR: Normal odor of stool is due to indole
and skatole formed by intestinal fermentation
and putrefaction
Odor varies according to the pH of the stool
BLOOD AND MUCUS IN STOOL: Observed in
either amebic dysentery or bacillary dysentery
PARASITES: Stool sample may show adult
worms/segments of worms(eg. roundworm,
pinworm, whipworm, hookworm or
tapeworm)
10/29/2021 8
Analysis of Stool Examination

9. CHEMICAL EXAMINATION
The chemical examination of stool includes:
REACTION AND pH
Normal stool pH: Ranges from 5.8 to 7.5
Strongly acidic stool: Observed with excess
carbohydrate diet or fermentation due to
lactose intolerance
Strongly alkaline stool: observed with excess
proteins in diet
10/29/2021 9
Analysis of Stool Examination

10. OCCULT BLOOD: Small amount of blood in stool cannot
be seen as gross examination
Chemical test is necessary to detect occult blood in
stool
Presence of blood/hemoglobin in the stool which is
detected by a ‘chemical test’ and not by the naked eye
is known as ‘occult(hidden) blood’
TEST FOR OCCULT BLOOD
• Benzidine test: sensitive test
• Principle: Heme compounds derived from hemoglobin
molecule in red cells(from blood in the stool) have
peroxidase activity.
• This peroxidase converts hydrogen peroxide(present in
the reagent) to nascent oxygen
10/29/2021 10
Analysis of Stool Examination

11. The released oxygen oxidizes the benzidine (in the
reagent) in an acidic pH to colored oxidation products
which are blue or green in color
PROCEDURE
The benzidine reagent consists of 4g benzidine base in
10ml glacial acetic acid
Stable for 2-4 months
Emulsify a bit of stool in 5ml water
Mix 1ml of emulsion with 1ml of benzidine reagent in a
test tube
Add several drops of 3% hydrogen peroxide
Interpretation - Appearance of blue color indicates the
presence of blood
Precaution - Benzidine is carcinogenic
Other test - Guaiacum test using gumguaiacum
10/29/2021 11
Analysis of Stool Examination

12. Causes of false –positive reactions:
Presence of substances like myoglobin and hemoglobin
(Presence in red meat) in diet
Presence of vegetable peroxidases (eg.Horse radish,
bananas, black grapes,pears, plums, melons)
Leukocytes and bacteria
Drugs like boric acid, bromides, iodine and oxidizing
agents.
Cause of false –negative reactions:
Use of vitamin C and other oxidants
SIGNIFICANCE
Determining the cause of microcytic hypochromic
anemia due to chronic blood loss
Cause of chronic blood loss may be:
GIT neoplasms(eg. colon, stomach cancer)
10/29/2021 12
Analysis of Stool Examination

13. Ulcerative diseases of the GIT
Hookworm infection
Drugs like aspirin, steroids and indomethacin
can be associated with increased
gastrointestinal bleeding
OTHER CHEMICAL TESTS
Quantitative fecal fat estimation: Increase in
fecal fat (more than 6g per day) is found in
malabsorption syndromes or diseases of
pancreas.
Presence of reducing substances like lactose in
stool may be found in infants with diarrhea
10/29/2021 13
Analysis of Stool Examination

14. 10/29/2021 Analysis of Stool Examination 14
Characteristics Amoebic dysentery Bacillary dysentery
Nature of stool Blood and mucous mixed
with fecal matter
Blood and mucous without
fecal matter
Consistency Does not adhere to the
container
Adheres to the container
Odor Offensive Odorless
Reaction Acidic Alkaline
Microscopy
RBC’s
Pus cells
Macrophages
Parasites
Charcot –Leyden crystals
In clumps
Scanty
Scanty
Trophozoites
Present
Discrete
Plenty
Plenty
Nil
Absent

15. MICROSCOPIC EXAMINATION
A fresh sample of stool without any
contamination with disinfectants is used for
microscopic examination
On microscopy, examine the stool for:
Leukocytes(pus cells), red blood cells, muscle
fibres, fat globules, crystals, cysts and yeast cells
and are expressed as number seen per high power
field
Protozoa, eggs, larvae and cysts of parasites,
flagellates and ciliates
They are reported as scanty, few, moderate or
many
10/29/2021 15
Analysis of Stool Examination

16. MICROSCOPIC EXAMINATION
Methods for the preparation of stool for
microscopy
Saline preparation
A small amount of stool sample is picked up with
the help of tooth pick and taken on a glass slide.
Mix with normal saline to make a thin emulsion
so that the fine print can be seen through it Cover
with a cover slip
This is useful for the demonstarion of motility
especially of Entamoeba histolytica
10/29/2021 16
Analysis of Stool Examination

17. IODINE PREPARATION
Gram’s Iodine is used instead of saline
Iodine imparts brown color to chromatin
granules (nuclei ) of amoebic cysts and also
glycogen vacuole
But iodine kills living parasites thereby
preventing identification of motility
10/29/2021 17
Analysis of Stool Examination

18.  STOOL CONCENTRATION
 When ova and cysts are few in number and are
not detected by routine methods, concentration
method will be of help
 These methods are as follows:
Floatation method:
Stool sample is mixed with either zinc sulphate or
magnesium sulfate which has a high specific
gravity and causes the parasite to float in the
solution
Used for concentration of cysts, larvae and most
of the helminthes eggs
10/29/2021 18
Analysis of Stool Examination

19. MICROSCOPIC EXAMINATION
Sedimentation methods:
 The parasites sediment and get deposited at the bottom by
centrifugation
 It can be done by either simple sedimentation method or by formal
– saline ether sedimentation method
 Simple sedimentation method: A small amount of stool sample is
mixed with saline in a tube or bottle and sleved through a strainer
 The sieved contents are centrifuged and the supernatant fluid
discarded
10/29/2021 19
Analysis of Stool Examination

20. The deposit is resuspended in more saline, mixed
and centrifuged
This is repeated till the supernatant fluid appears
clear
The deposit is examined directly on a glass slide
The sieved contents are centrifuged and the
supernatant fluid discarded
The deposit is resuspended in more saline, mixed
and centrifuged
This is repeated till the supernatant fluid appears
clear
The deposit is examined directly on a glass slide
10/29/2021 20
Analysis of Stool Examination

21. Formal- saline ether sedimentaion method:
• This yields a good concentration of parasites
and is recommended for routine work
• But this method cannot be used to
concentrate living parasites because the
formalin used kills the parasites
10/29/2021 21
Analysis of Stool Examination

22. STOOL CULTURE AND SENSITIVITY
Collection - for culture should be collected in a sterile wide
mouthed container
Culture Media used - Mac conkey’s agar ,nutrient agar or selective
media depending on the suspected organism
Procedure:
 Take stool in culture media and incubate at 37C for 18-20 hours
 Suspected colonies are tested by using oxidase test
 Causative organisms are identified by using biochemical tests
 Organism may be confirmed by agglutination using specific antisera
 Antibiotic sensitivity testing is done for the identified pathogenic
organism
10/29/2021 22
Analysis of Stool Examination