Biomedical Investigation: Stool Examination

Biomedical Investigation & Laboratory Practices: General Stool Examination

• A stool analysis is a series of tests on a stool sample to diagnose digestive tract conditions.
• Stool analysis may be performed for patients with abdominal pain, diarrhea, anemia, poor growth, abnormal stool color, or skin conditions like urticaria related to parasitic infection with helminthes.

Collection of Fecal Specimens

• Collect 10-15 grams of stool in a dry, clean container. Avoid urine, water, soil, or other materials.
• If feces cannot be collected, use a cotton swab inserted into the rectum for about 10 seconds.
• Label the specimen with patient, date, and time of collection and send with a request form to the lab as soon as possible.
• Fresh stool should be examined immediately or preserved.

Macroscopic Stool Examination

• Color:

  • Normal: Brown (due to stercobilin and urobilin from bilirubin breakdown)
  • Abnormal: Black (iron medication, upper GI bleeding)
  • Bright red: Lower GI bleeding (piles, anal fissure)
  • Clay/gray-white: Obstructive jaundice
  • Pale brown: Pancreatic deficiency (fat malabsorption)
  • Yellow-green: Lack of normal intestinal flora or rapid transit of feces
  • Red-brown: Drugs (Tetracyclines, Rifambicin)
  • Note: If black stool and no iron medication, a false occult blood test is recommended.

• Odor:

  • Normal: Offensive (due to bacterial breakdown of substances like skatole, mercaptans, indole, and hydrogen sulfide)
  • Abnormal: Very offensive with constipation, excessive gas, bacterial infection, or malabsorption (foul-smelling stool indicates steatorrhea)
  • Note: Spicy food can affect stool odor

• pH:

  • Normal: Variable (dependent on diet and bacterial fermentation in the small intestine)
  • Abnormal: High alkaline (high protein diet, secretory diarrhea, colitis, antibiotic use with impaired colonic fermentation)
  • High acidic (high carbohydrate diet, poor fat/sugar absorption)
  • Note: Breast-fed infants have slightly acidic stool; bottle-fed infants have slightly alkaline stool.

• Consistency:

  • Normal: Normally well-formed
  • Abnormal:
    • Very hard: constipation
    • Semi-formed: parasitic infection
    • Loose/Soft: Parasitic infection, diarrhea
    • Watery: Bacterial infection

Microscopic Stool Examination

• Gross blood:

  • Normal: No visible blood
  • Abnormal: Fresh blood (hematochezia) in lower GI bleeding, bright red blood per rectum (BRBPR). Mixed or not mixed with stool -Causes: ulcerative colitis, colorectal cancer, schistosoma infection, anal fissure, piles.

• Naked eye parasite:

  • Normal: No parasites or larvae visible.
  • Abnormal: Whole worm or segments visible.
  • Examples: Ascaris lumbricoides, Enterobius vermicularis (pinworm), examples of two worms.

• Other findings:

  • Yeast: blastocystis hominis (harmless yeast cells)
  • Crystals: Triple phosphate, calcium oxalate, cholesterol (due to food ingestion)
  • Fibers: Undigested plant material
  • Air bubbles: Normal, no clinical significance
  • Oil droplets: Normal, bright, completely rounded. (can be muddled with cysts, but cysts are not as bright and not rounded.)
  • Undigested food: Pollen-grain, vegetable shapes.
  • Bacteria: Usually non-pathogenic (E. coli, Lactobacillus)
    • Note: Pathogenic bacteria (Salmonella, Shigella, Staphylococcus aureus) can cause pus and require stool culture for differentiation.

Procedure

• Place saline, or iodine, on the slide.
• Collect a small amount of stool material using an applicator stick.
• Emulsify the material in the saline/iodine.
• Cover with a cover slip.
• Examine under low (10x) and high (40x) power.
• Examine the entire preparation for eggs, larvae, and protozoa.
• Collect samples from multiple stool areas, especially bloody or mucoid areas.