The faeces are normally, composed of 25% of faecal matter while rest of it is water. In certain diseases, the faeces may contain such substances which are not normally present in healthy individual such as blood, mucus, parasites, intestinal calculi, pus, and pathogenic organisms (bacteria, fungi and viruses), etc.
The amount of adult stool is nearly 150 to 250 gms /day. Stool should be collected in a clean, dry covered container and should not be mixed with urine.
The stool should be examined for macroscopic examination, Chemical examination, and Microscopic examination.
Stool should be examined macroscopically for following points:
Normal stool is light, or dark brown in colour. Following abnormal colours are found:
Green — in infantile diarrhoea.
Clay— in obstructive jaundice, excess of fat, tuberculous peritonitis.
Dark brown or bright red— bleeding from distal colon.
Streaks of bright red blood— Piles, Fissures, Carcinoma of Rectum.
Black— Gastrointestinal bleeding. T.B.
Odourless after use of oral antibiotics, foul smelling in acute enteritis, malignant ulcer in rectum and distal colon.
Mucus is seen in bacillary dysentery.
Pus with blood and mucus present in ulcerative colitis, bacillary dysentery, regional enteritis.
Gall stones may be seen in faeces.
Impart a dark red to black colour and a terry consistency.
Segments of Tapeworm and Roundworm may be seen in respective infections.
Normally, pH of stool is 6.8 to 7.3 on mixed diet. Excess of carbohydrate diet produces acidity and excess of proteins produce alkalinity.
Saline or iodine preparation should be made and examined with the low and high power objectives.
Various ova or cysts may be seen as abnormal constituents of stool. This includes ovas of following parasites:
i. Hook worm
ii. Ascaris (Round Worm)
iii. Trichuris trichuria
iv. H. nana
vi. E. Vermicularis
1. Vegetable cells and fibers— in case of indigestion.
2. Starch granules— in carbohydrate dyspepsia.
3. Muscle and elastic fiber.
4. Fats and fatty acids in fatty dyspepsia.
5. Cells— abnormal cells in stool includes— epithelial, pus cells, macrophages, short cells, eosinophils, RBCs.
The abnormal crystals includes:
a. Calcium oxalate, Triple phosphate crystals, fatty acid crystals.
b. Needle shaped crystals is seen in ulcerative conditions of intensive dysentery, malignant ulcers, etc.
Besides these, various bacteria, protozoa, metazoa, yeast and fungi may also be seen in stool examination.
Concentration Methods for Ova and Cyst:
Take about one gram of faeces and thoroughly emulsify with super saturated sodium chloride solution in water in a suitable container. The container should have diameter as well as depth of about one inch. The container is so filled with the emulsion that a slide placed on it just touches the preparation.
The slide is kept in this position for about 25 minutes, and gently inverted. Ova of many helminths will float and stick to the slide. A cover-slip is placed on the slide and the preparation is examined under the low power of microscope.
Occult Blood Test:
Make a suspension of faeces and boil for two minutes to destroy, oxidize and inactivate bacteria or enzymes. Cool and add 2 ml of saturated solution of benzidine in glacial acetic acid, mix well and add 1 ml (30%) hydrogen peroxide. Orthotoludine or Guiac solution can be used instead of benzidine solution.
A deep blue colour indicates the presence of haemoglobin.
The presence of blood in the stool is of great significance in diagnosing the disease of inflammatory, neoplastic or ulcerative origin of gastro-intestinal tract.
Iron may affect the test, so patient should not take meat diet, green vegetable, or iron in any form.