Stool Examination:- Part 2 – Normal Stool Findings
- 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 the stool needed for the examination is 2 to 5 grams.
- Advise patients for the following things for at least 48 hours before the collection of the stool:
- Avoid mineral oils.
- Do not take bismuth.
- Antibiotic s like tetracyclines.
- Anti-diarrheal drugs which 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 at least 48 hours before the collection.
- Warm stools are better for the ova and parasites.
- Don’t refrigerate the stool for ova and parasites.
- Stool 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 the collection of the stool.
Stool preservatives are:
- Preservatives for the wet preparation are:
- 10% formol-saline for the wet preparation. This is the best preservatives 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.
The normal findings in the stool:
- 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 has also 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.
- 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 there are more than 100 ml of blood 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.
- Microscopic Examination:
- Normally RBCs are absent.
- Epithelial cells are present and these are increased with GI tract irritation.
- Few WBCs are seen and these may be increased due to GI tract inflammation.
- 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 0 to 2 +.
- Hematoidin crystals are sometimes seen after GI tract hemorrhage.
- This is normally found 40 to 280 mg / 24 hours.
- Normally absent and this is less than 7 grams / 24 hours during three days period.
- This is less than 30% of dry weight (This is 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 hour’s.
- Stercobilinogen normally is 40 to 280 mg/day with an average of 150 mg/day.
- Nitrogen depends upon the nature of the diet.
- The normal amount is 1 to 1.5 g/day.
- Coproporphyrin’s normal amount is 300 to 1100 µg/day.
Summary of the normal stool:
|Physical character||Normal values|
|Gross||May see vegetables, seeds, and fibers|
|Odor||Variable depends upon the bacterial fermentation|
|Consistency||Variable soft to semiformed|
|Amount||100 to 200 g/day|
|pH||Neutral and maybe 7.0 to 7.5|
|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|
|Potassium||15.7 to 20.7 meq/day|
|Calcium||Roughly 0.6 gm/24 hours|
|Chloride||2.5 to 3.9 meq/day|
|Trypsin||20 to 95 U/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|
In routine stool examination consists of:
- Direct wet film.
- Concentration method.
- Permanently stained slide.
- The following drawing shows how to make a thin smear for permanent stain.
- Note: Stool study is continued.