Stool Examination:- Part 1 – Normal Stool Examination Findings
Normal Stool Examination
Sample for stool examination
- The fresh stool can be examined immediately for the moving organisms.
- Stool in 10% formalin can be used for Helminths and protozoa.
- Stool in formalin-ethyl acetate is used to concentrate the stool.
- The smallest amount of stool needed for the examination is 2 to 5 grams.
- For ova and parasites, there are three methods:
- Direct stool examination.
- Concentration method.
- The permanent stain of the stool.
Samples for various parasitic infestations:
|Sample for testing||Possible diagnosis|
Precautions for stool examinations:
- Advise patients for the following things for at least 48 hours before the collection of the stool:
- Avoid mineral oils.
- Do not take bismuth.
- Don’t take antibiotics like tetracyclines.
- Anti-diarrheal drugs are non-absorbent.
- Avoid anti-malarial drugs.
- The patient should not have a barium swallow examination before the stool examination.
- For occult blood, stop iron-containing drugs, meat, and fish 48 hours before the collection.
- Warm stools are better for the ova and parasites.
- Don’t refrigerate the stool for ova and parasites.
- Stools for ova and parasites can be collected in formalin and polyvinyl alcohol. These are used as a fixative.
- If there is blood or mucus, that should be included in the stool because most of the pathogens are found in this substance.
- Exam the stool before giving antibiotics or other drugs.
- The semi-formed stool should be examined within 60 minutes of collection.
- The liquid stool should be examined within the first 30 minutes.
- The solid stool should be examined within the first hour of collection.
- Trophozoites degenerate in liquid stool rapidly, so exam the stool within 30 minutes.
- In the case of constipated cases, use non-residual purgative on the night before collecting the stool.
Indications for stool examination:
- To evaluate the function and integrity of the GI tract.
- To rule out the presence of WBCs and RBCs.
- To find ova or parasites.
- To see the presence of fat for malabsorption syndrome.
- For screening for colon cancer.
- For asymptomatic ulceration of GI tract.
- Evaluate diseases in the presence of diarrhea and constipation.
- Summary of stool studies are done to evaluate:
- Intestinal bleeding.
- Inflammatory diseases.
- Different causes of diarrhea.
Stool preservatives are:
- Preservatives for the wet preparation are:
- 10% formol-saline for the wet preparation. This is the best preservative as it kills the bacteria and preserves the protozoa and helminths.
- Sodium acetate formalin.
- Methionate iodine formalin. This is a good preservative for the field collection of the stool.
- For staining, use Polyvinyl alcohol.
- Avoid preservatives for the culture of stool.
- Usually, three parts of the preservatives and one part of the stool.
Gross Stool examination includes:
- Concretions (gallbladder stones rarely may be found).
Undigested food particles like:
- Vegetable cells.
- Vegetable fibers.
- Plant hairs.
- Amorphous vegetable material.
- Pollen grains are regular in size and often present in large numbers.
- These are usually light brown. Sometimes it may show striations.
- Meat fibers and muscle fibers are seen in the stool. Their presence shows defective indigestion.
- The increased amount of meat fibers is found in:
- Malabsorption syndrome.
- A pancreatic functional defect like cystic fibrosis.
- The increased amount of meat fibers is found in:
- It may be spherical if undigested; then, they have concentric layers of white, homogenous material.
- On the stool smear, do the gram stain and see the bacteria. Normally there are bacteria in the stool.
Desquamated epithelial cells:
- This depends upon the size of nuclei and the cytoplasm. These are usually from the anal canal mucosa.
- When stained, smears may show a nucleus divided into four separate spheres with peripheral chromatin.
- Also, show an apparent karyosome.
- The nuclear material is larger in proportion to the amount of cytoplasm compared to the amoebic cyst.
- The shapes of the nuclei are variable.
- Thes have numerous inclusions in the dark staining cytoplasm.
- These need to differentiate from the intestinal amoebae. There are large particles in the cytoplasm.
- The nucleus has no karyosomes.
- Degenerated macrophagic cells lost their nucleus and have few ingested materials.
- Also, the nucleus has a fine network of chromatin and large particle scattered.
Digestive tract products:
- Digestive tracts products like:
- Bile pigments products.
- Digested but not absorbed food.
- Products produced by the decomposition of the stool are:
- Various gases like H2S, CO2, and nitrogen.
Macroscopic or gross appearance of the stool:
- The gross findings of the stool are important. Note the consistency and the color of the stool.
- Try your best to examine the stool as received in the lab. In case of delay, use the preservatives.
- The mushy or liquid stool may suggest the presence of protozoan trophozoites. If the stool is examined, within one-half hours gives the best result.
- Helminth eggs and larvae are found in the liquid or formed stool. Grossly you may see proglottids or adult tapeworms.
Physical character and appearance:
|Physical characters||Macroscopic (Gross) appearance|
The consistency of the Stool (gross appearance):
- Normal is soft and formed.
- Loosely formed stools.
- Watery stools.
- Thin stools.
- Pellet-like stools.
- Dry or hard stools are found in constipated patients.
- Puttylike stools.
- The small round hard stool is due to habitual constipation.
- Pasty stools are due to high-fat contents and are seen in:
- common bile duct obstruction.
- In Celiac disease, the stool looks like aluminum paint.
- Cystic fibrosis due to pancreatic involvement and are greasy.
- Diarrheal stools are watery.
- Steatorrhea stool is:
- Large in amount.
- Constipated stools are firm and may see spherical masses.
- Ribbon-like stool suggests the spastic bowel, rectal narrowing, stricture, or partial obstruction.
- The very hard stool is due to excessive water absorption due to prolonged contact with colonic mucosa.
- The normal color is due to the presence of stercobilinogen and is brown.
- Yellow or yellow-green color is seen in diarrhea.
- Black and tarry (related with consistency) stools are due to bleeding of the upper GI tract from tumors.
- The maroon or pink color is from the lower GI tract due to tumors, hemorrhoids, fissures, or inflammatory processes.
- Clay-colored stools are due to biliary tract obstruction.
- Mucous in the stool indicate constipation, colitis, or malignancy.
- Pale color with a greasy appearance is due to pancreatic deficiency leading to malabsorption.
Causes of different colors of the stool:
|The color of the stool||Causes|
|1. Brown, dark brown, or yellow-brown||Normal color is due to the oxidation of bile pigments.|
|2. Gray color||Ingestion of chocolate or Cocoa. Steatorrhea.|
|3. Green color||Ingestion of spinach, and chlorophyll vegetables, administration of calomel.|
|4. Black (Taary black)||Iron or bismuth ingestion, bleeding from the upper GI tract.|
|5. Very dark brown||Diet high in meat.|
|6. Red color||Diet high in beats, laxatives of vegetable origin, Bleeding from the lower GI tract.|
|7. Green or yellow-green||Diet high in spinach and green vegetables.|
|8. REd streaks of blood on feces||Bleeding from the hemorrhoids, fissure, ulcerative lesion, or carcinoma of the rectum or anus.|
- Normally there is 100 to 200 G/day.
- With a vegetable diet, maybe 250 g/day.
- Many disorders cause large, bulky stools, even in people who don’t eat a lot.
- Like malabsorption syndrome and carbohydrate indigestion.
- Your stool size has more to do with how well you digest your foods than what you eat.
- Some foods produce larger stools because they don’t break down completely.
- Some gastrointestinal disorders also cause poor food breakdown and absorption, which leads to large, bulky stools.
- The foul odor is caused by the undigested protein and by excessive intake of carbohydrates.
- Stool odor is caused by indole and skatole, formed by bacterial fermentation and putrefaction.
- A bad odor is sickly produced by undigested lactose and fatty acids.
- The odor is increased due to excess intake of proteins.
- The putrid odor is due to severe diarrhea of malignancy or gangrenous dysentery.
- The mucosa of the colon produces mucus in response to parasympathetic stimulation.
- Pure mucous is translucent, gelatinous material clinging to the stool’s surface. This may be seen in:
- Severe constipation.
- Mucous colitis.
- Excessive straining of the stool.
- Emotionally unstable patient.
- Mucus in diarrhea with microscopically present RBCs and WBCs are seen in:
- Bacillary dysentery.
- Ulcerative colitis.
- Intestinal tuberculosis.
- Acute diverticulitis.
- Ulcerating malignancy of the colon.
- Mucus with blood that is clinging to stool is seen in:
- Malignancies of the colon.
- Inflammatory lesion of the rectal canal.
- An excessive amount of mucus was seen in:
- Villous adenoma of the colon.
- This depends upon the dietary intake.
Stool physical character and possible causes:
|Stool findings (Physical features)||Possible Causes|
|1. Diarrhea mixed with blood and mucous||Typhoid, Amoebiasis, and large colon carcinoma|
|2. Diarrhea mixed with Pus and mucous||Ulcerative colitis, Salmonellosis, Intestinal tuberculosis, Shigellosis, Regional enteritis, and acute diverticulitis|
|3. Patty stool with high-fat contents||Cystic fibrosis and CBD – obstruction|
|4. Formed stool with attached mucous||Constipation, Mucous colitis, and excessive straining|
|5. Small, hard dark balls like||Constipation|
|6. Clay-colored, pasty, and little odor||Bile duct obstruction and barium ingestion.|
|7. Black, tarry, sticky, watery, voluminous||Upper GI tract bleeding, Non-invasive infections like Cholera, Staphylo. coccal food poisoning, Toxigenic E. Coli, and Disaccharidase deficiency|
The chemical examination includes:
- Stool pH.
- Reducing substances.
- For occult blood.
- Presence of fat, carbohydrate, and proteins.
- Normally stool is slightly acidic or alkaline, or neutral.
- pH is 7.0 to 7.5, depending on the diet.
- Newborn pH = 5.0 to 7.5.
- The pH of the stool depends upon the diet and bacterial fermentation in the small intestine.
- Carbohydrate changes the pH to acidic while the protein breakdown changes to alkaline.
- The breastfed infant’s pH has a slightly acidic stool.
- Bottle-fed infants have a slightly alkaline stool.
- The pH stool test helps to evaluate carbohydrate and fat malabsorption.
- pH stool also helps to know disaccharidase deficiency.
- Alkaline (Increased pH) stool is seen in:
- Villous adenoma.
- Antibiotic therapy.
- Excess intake of proteins.
- Acidic (Decreased pH) stool seen in:
- Fat malabsorption.
- Disaccharidase deficiency.
- Carbohydrate malabsorption.
- Excess intake of carbohydrates.
- Precautions for pH estimation:
- Barium intake and laxatives change the pH.
- If the specimen is contaminated with urine, we will need to discard the sample.
Presence of Fat:
- The fat in the stool shows the possibility of :
- Deficiency of pancreatic digestive enzyme.
- Deficiency of Bile.
- This is normally found 40 to 280 mg/24 hours (100 to 400 Ehrlich units/100 gm).
- 400 to 1000 mg/24 hours.
- Normally absent, which is less than 7 grams / 24 hours during three days period.
- This is less than 30% of dry weight (On a diet of 50 grams of fat per day).
- 2 to 6 grams/24 hours (7 to 21 mmol/day).
- This is about 0.6 gram / 24 hours.
- It is normally 40 to 280 mg/day with an average of 150 mg/day.
- It depends upon the nature of the diet.
- The normal amount is 1 to 1.5 g/day (<2.5 gram/day).
Microscopic stool Examination:
- Presence of leukocytes (pus cells).
- Presence of Red Blood Cells.
- Ova and parasites.
- Presence of meat fibers and muscle fibers.
- Presence of fat.
- Yeast and molds.
Presence of Leukocytes:
- Normally, there are no WBCs.
- WBCs only appear in infection or inflammation.
- Their presence is important in case of diarrhea or dysentery.
- >3 WBCs /high fields are seen in ulcerative colitis and bacterial infection.
- Greater numbers of WBCs indicate invasive pathogens.
- Viruses and parasites don’t cause the presence of WBCs in the stool.
- Increased number of WBCs seen in the stool:
- Bacillary dysentery.
- Chronic ulcerative colitis.
- Salmonella infection.
- Yersinia infection.
- Invasive E.coli diarrhea.
- Fistula of anus or rectum.
- Localized abscess.
- Few WBCs are seen in amoebiasis.
- Also, WBCs are seen in typhoid.
The absence of WBCs seen in some of the diarrhoeal conditions alike:
- Viral diarrhea.
- Drug-induced diarrhea.
- Amoebic colitis.
- Non-invasive E.coli diarrhoea.
- Parasitic infestation.
- Toxigenic bacterial infection.
Presence of Red Blood Cells in the stool:
- Normally RBCs are absent.
- Epithelial cells are present, and these are increased with GI tract irritation.
- Few WBCs are seen, which may be increased due to GI tract inflammation.
- Blood in the stool can be:
- Bright red from the bleeding in the lower GI tract.
- Maroon in color.
- Black and tarry from bleeding from the upper GI tract.
- Occult blood (not visible to the naked eye).
- Causes of blood in stool:
- Make a smear from the mucus area or the blood-colored area from the watery or semiformed stool.
Presence of crystals and other substances:
- Crystals of calcium oxalate, fatty acids, and triple phosphate are commonly present.
- Charcot-Leyden crystals are seen in parasitic infestation, especially in amoebiasis.
- Undigested vegetable fibers and meat fibers are seen sometimes.
- Neutral fat globules stained with Sudan may be seen normally at 0 to 2 +.
- Hematoidin crystals are sometimes seen after GI tract hemorrhage.
Ova and parasites:
- Normally there are no parasites or eggs in the stool sample.
- Multiple stool samples are needed to rule out the parasitic infestation for at least three consecutive days.
- An abnormal result means parasites or eggs are present in the stool. Such infections include:
- Roundworms: Ascaris lumbricoides.
- Hookworms: Necator americanus.
- Pinworms: Enterobius vermicularis.
- Whipworm: Trichuris trichiura.
- Tapeworms: Diphyllobothrium latum, Taenia saginata, and Taenia solium.
- Protozoa: Entamoeba histolytica (an amoeba) and Giardia lamblia (a flagellate)
Summary of the normal stool examination:
|Physical character||Normal values|
|The water content of stool||It is up to 75%|
|Gross||May see vegetables, seeds, and fibers|
|Odor||Variable depends upon the bacterial fermentation|
|Consistency||Variable soft to semiformed|
|Reducing substances||Negative <0.25 g/dL|
|Neutral fat globules||Normal = 0 to 2+ seen with Sudan black stain|
|Urobilinogen||50 to 300 mg/day|
|Sodium||5.8 to 9.8 meq/day (10 to 20 meq/Kg)|
|Potassium||15.7 to 20.7 meq/day (5 to 20 meq/Kg )|
|Calcium||Roughly 0.6 gm/24 hours|
|Chloride||2.5 to 3.9 meq/day|
|Trypsin||20 to 950 units/g|
|Lipids (fats)||0 to 6 g/day (<7 gm/24 hours during 3 day period)|
|Osmolality||200 to 250 mOsm|
|Ova and cyst||Negative|
|Undigested foods||Negative to a small amount|
|Meat fibers, starch||Negative to a small amount|
The summary of normal findings in the stool examination:
- The bulk of the stool is 100 to 200 grams.
- It may be up to 250 grams on a vegetable diet.
- Amount of water
- Normally there is up to 75 % of the water in the stool.
- It is interesting that our body also has roughly 75% of water.
- Gross appearance
- Normal is soft and formed.
- Scanty mucous seen.
- Abundant mucous seen.
- Mucous with blood seen.
- Grossly fibrous.
- Homogenous appearance.
- The normal color is yellowish-brown due to the presence of bilirubin and bile.
- In infants, the color is green, and the stool is loose or pasty.
- Various colors depending on diet.
- Clay color stool is seen in biliary obstruction.
- Tarry stool is seen if more than 100 ml of blood is coming from the upper GI tract.
- The red color is seen due to blood in the large intestine or undigested beets or tomatoes.
- The black color stool is seen due to blood, iron, or bismuth medication.
- Consistency may be:
- Watery like a fluid.
- This is from 7.0 to 7.5.
- This may be acidic with high lactose intake.
In routine stool examination consists of:
- Direct wet film.
- Saline: Can make a smear with normal saline.
- Check the clarity of the saline solution, microscopically.
- Iodine preparation is used for the identification of the cysts in the stool.
- Keep iodine solution in the dark brown bottles with a tight cap.
- Methanol is used to fix the slide.
- Concentration method.
- Permanently stained slide.
- The stained slide can be preserved by the use of the DPX, permount, or Hystomount.
- Place a drop of the above preservatives over the stained slide and leave it to dry.
- After drying remove the excess of the mount.
- These smears can be kept for several years.
- The following drawing shows how to make a thin smear for a permanent stain.
Examples of some of the parasites:
Important facts about the stool examination:
- The intestinal protozoan is usually found in soft and liquid stool.
- Cysts are rarely found in liquid stool.
- Cysts are found in the formed stool.
- Helminth eggs are found in liquid or formed stool.
- Liquid stools are diluted, so difficult to find these parasites.
- Examined the surface of the unpreserved stool for macroscopic parasites.
- Pinworms are seen at the surface and tapeworms in the interior of the stool.
- The freshly passed stool is essential for the detection of amoebae or flagellate.
- Should examine all liquid or soft stool within 30 minutes of the collection.
- Formed stool immediate examination is not critical; it can wait for 3 to 4 hours.
Questions and answers:
Question 1: What is the normal pH of the stool.
Normal pH of the stool varies according to the diet. it is neutral and maybe 7.0 to 7.5.
Question 2: What is the effect of the high fiber diet.
The bulk of the stool increases to 500 g.
Question 3: How much fats goes in the stool.
It is 0 to 6 g/day.
Question 4: Which crystal is seen in parasitic infestation in the stool.
It is Charcot Leyden crystal.
- Note: Stool study is continued.