Laboratory Feces Flashcards
What are the instruction to collect a specimen ?
In a clean container, not contaminated by urine or toilet water. Transfer it to the laboratory container.
What kind of Colors can the stool be ?
Brown, pale (white), black, red, green.
What cause the brown color of stool ?
The breakdown product of hemoglobin, bilirubin is added to bile when it passes in the liver. In the small intestine it is converted into urobilinogen then reduced to stercobilinogen. Then stercobilinogen is oxidized into stercobilin which give the stool its brown color.
The stool also contaisn another bilirubin derivative called urobilin.
What cause a pale/white stool ?
When there is no or not enough derivative of bilirubin in the stool (stercobilin and urobilin), the coloration of it is paler.
It may signify a blockage of the bile duct or difficulties in the production of bile by the liver.
What cause the black stool ?
When there’s an upper GI tract bleeding (oesophagus, stomach, duodenum). It takes the blood then around 3 days to reach the stool. By then it will have been degraded to stercobilin. Because of the high concentration of bilirubin product in the stool it will be darker than usual.
Black color can also be caused by ingestion of iron, charcoal and bismuth.
What causes red stool ?
When there’s an lower GI tract bleeding. The blood reach the stool in less time and this doesn’t have the time to be degraded. It keeps its origina color in the stool.
It can also be due to the ingestion of too much beets.
What causes green stool ?
Some oral antibiotics can cause the oxidation of bilirubin to biliverdin.
Ingestion of a lot of green vegetables of food coloring can also be the cause.
What does the appearance of the stool tell you ?
Watery consistency : diarrhoea
Small and hard : constipation
Slender ribbon like : obstruction of normal passage
Pale bulky and frothy with a foul odor : biliary obstruction
Mucus coated stool : intestinal wall or irritation.
What causes mucus coated stool ?
Pathological colitis or excessive straining during elimination.
When there’s also blood it may be a damage to the intestinal wall caused by a bacterial or amebic inflammation.
Why and how to you do a microscopic examination of the stool ?
It is used to detect leucocytes associated with diarrhoea and undigested muscle fibers and fats.
Fecal leucocytes are only seen in the feces if they affect the intestinal mucosa.
What is occult blood ?
Occult blood is the hidden blood, present in the stool but that doesnt give it its color.
Blood is pathologically significant from 2,5 mL/ 150 g but at that point there’s not visible signs.
Finding occult blood help in the detection of colorectal cancer.
How do you detect occult blood ?
Do a screening test based on the detection of pseudoperoxidase activity.
When haemoglobin react with hydrogen peroxide it oxidase it transforming a colourless compound into a coloured one.
You can use indicator chromogène for that like guaiac that show a blue color when there’s blood / pseudoperoxidase activity present.
What could cause error in the detection of occult blood ?
False positive : aspirin or anti-inflammatory medication, red meat, horseradish, raw brocoli, cauliflower, radishes, turnips, melons, period.
False negative : vitamin C and iron supplement (often with vit C)
Dysentery ?
Infection of the intestine causing diarrhea with blood or mucus
What is TFT ?
Triple feces test used to confirm the presence of intestinal parasite. Indicated in case of diarrhea, nausea or vomiting.
Weight of feces with normal western diet ?
100 - 250 g / day
What cause the rotten egg smell of feces ?
Poorly digested protein
What cause the butyrique acid smell ?
The poor digestion of fat.
Normal pH of feces ?
Adult +- 6.6
Infant +- 5.3
What is the occult blood used to detect ?
Colon cancer suspicion (risk increased for +60 patients). The polyps (1st development stage of cancer) might bleed but not enough to see it clearly.
iFOBT ?
Immunochemical fecal occult blood test. The most commonly performed lab test.
How do you do a stool microscopy ?
If suspicion of egg worm you use a scotch tape preparation.
Then use different coloration :
Methylene blue : highlight the leucocytes in dark blue and the plasma is light blue
Eosin : alive parasite will not get coloured orange contrary to the rest of the sample.
Sudan : the fat will be coloured orange.
Protozoa in feces ?
Are single cell microscopic animal. The most common pathogenic one in the netherlands is giardia lamblia.
Meconium stool ?
First stool of the baby after birth. Contains the blood the baby may have ingested during birth. Doesn’t have bacteria thus doesn’t smell.
It is black, leaky but not smelly.
Transitional stool ?
Present for a few days after birth depending on how much blood the baby has ingested. The baby is only drinking milk.
Doesn’t have an horrible smell.
Stool of infant ?
If exclusively breastfeed : yellowish color
If fed using extensively hydrolysed formula : more brownish color and more consistent.
Physiological stool ?
= normal stool
3-4 on the scale of bristol
Brown and smelly.
Steatorrhea diarrhea ?
Yellow stool that can take the form of the recipient.
You should ask yourself how the pancreas is working ?
Rice water stool ?
Liquid light but not transparent stool.
Patient suffer from cholera. You should beware of dehydratation.
Méléna stool ?
Black stool with shine looking like jam, has a rotten egg smell.
Signify a blood loss high in the intestine probably the stomach.
Amoebic dysentery ?
Mucus and blood in stool.
Could be a tropical disease, an infection of the liver.
Steatorrhea stool ?
Oily and creamy stool due to the large amount of fat.
Signify a parasite infection, maybe giardia lambia.
Scybala ?
Small stool like hard bullet. It is a hard constipation.
It may cause wounds around the anus : fissure ani.
Acholic stool ?
Clay coloured stool, often with dark brown/yellow urine.
Signify a bile duct obstruction (bilirubin does not go into the intestine resulting in a loss of brown color).
Ascaria, large roundworms ?
They can reach up to 10-20 cm and they stay in the intestine. They don’t really cause symptoms except ileus = obstruction of the intestine with a ball of worm. Before surgery of the intestine patient take medication to discard the worms.
Tapeworms ?
Usually living in the colon, they come from raw beef or pork meat.
While beef worm can only infect cow, pork worm can infect pigs and humans.
What kind of leucocytes do you find in the microscopy ?
PMN = polymorpho nuclear leucocytes
MN = monomorpho nuclear leucocytes.
If there’s more PMN it is an infection of the intestinal wall
What does it means if the stool is more concentrated ?
The person did not chew well.
What do you do after finding leukocytes with methylene blue ?
Do a microscopy to find out what type of leukocyte they are.
Polymorphonuclear : bacterial infection
Monomorphonuclear : parasite or viral
Technique of stool microscopy :
Drop of sodium chloride on the slide.
Take a bit of stool (large as a grain of rice)
Mix the two
Push the chunks of the stool to the side
Place the cover slip, push the chunks to the side while sliding the cover then drop it.
A gradient should appear : it will help to see at which thickness you can visualise things best.
