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Course: Clinical Analysis
Lecturer: Dr. Weam Saad
Lecture: Stool Tests
Stool Tests
These tests are usually ordered during diarrhea cases which last for few
days, there are only two tests most common in clinical laboratories:
1. Stool Analysis or General Stool Examination (GSE).
2. Stool Culture.
1. Stool Analysis or General Stool Examination (GSE).
The stool analysis is a series of tests done on the stool (feces) sample to
help in diagnosis certain conditions affecting the digestive tract. These
conditions can include infection (such as from parasites, viruses, or
bacteria), poor nutrient absorption.
For a stool analysis, the stool sample is collected in a clean container
and then sent to the laboratory. The analysis includes microscopic
examination by direct smear and sedimentation method, and several
chemical tests like pH. The fresh stool should be checked for color,
consistency, amount, shape, odor, and the presence of mucus.
The stool may be examined for blood (presence of RBCs), fat, meat
fibers, bile, white blood cells, and sugars and undigested food. If there is a
significant number of bacteria found then a stool culture must done.
During parasitic infections, detection for ova, cyst, larva or trophozoite
is of the importance than other components of patients stool sample.
Movement of trophozoite can be noticed during direct smear.
Sedmintation method can be done taking only the button sediments of
fresh stool mixed with 10% formalin and ethyl acetate then centrifuged.
This test usually used to diagnose parasitic infection by getting rid of other
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components of stool which have less gravity. The most common parasitic
infections are colitis due to Entamoeba histolytica and Giardia lambelia.
2. Stool Culture
The stool culture is done to identify bacteria or viruses that may be
causing an infection. Although more than 50 different kinds of bacteria
normally live in the intestines as normal flora, large numbers of abnormal
bacteria, viruses, fungi, or parasites can grow in the intestines and cause
infections and diseases.
For a stool culture, a stool sample is collected in a clean container and
placed under conditions that allow bacteria or other organisms to grow, only
one stool sample is needed, or several stool samples over a period of days
may be needed.
The type of infection is identified by noticing the growth, by performing
chemical tests on the stool sample, and by looking at the sample under a
microscope. The procedure of culturing is similar of that for urine culture.
Normal flora of Gastrointestinal Tract:
Bacteroides spp.
Enterococcus faecalis
Escherichia coli
Enterobacter spp.
Coliforms
Klebsilla spp.
Pathogens can be found during stool culture:
Bacteria:
Escherichia coli
Salmonella spp.
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Shigella spp.
Staphylococcus aureus
Clostridium spp.
Fungi:
Candida albicans
Viruses:
There is a wide broad viruses that cause enteritis and colitis e.g. Rotavirus.