M AUBF: FECALYSIS

• Fecalysis


  Examination of feces
• Feces

  Human feces, also called stool, is the waste residue of indigestible materials of an animal's digestive tract expelled through the anus during defecation
• Meconium


  Newborn's first feces
• Scatology or coprology


  The study of feces
• Bacterial metabolism


  • Produces strong odor and flatus
  • Lactose intolerance leads to excessive gas production
• Small intestine


  • Major site for final breakdown and reabsorption of compounds
• Digestive enzymes


  • Trypsin, chymotrypsin, lipase, and amino peptidase and lipase
• Diarrhea


  Increase in daily stool (above 200g), increased liquidity and frequency of more than three times per day
• Classification of diarrhea

  • Illness duration
  • Mechanism
  • Severity
  • Stool characteristics
• Major mechanisms of diarrhea

  • Secretory
  • Osmotic
  • Intestinal hypermotility
• Secretory diarrhea

  Caused by an organism that produces a toxin that stimulates adenylase cyclase enzyme, leading to crampy diarrhea and secretion of intestinal fluid
• Invasive diarrhea


  Caused by invasive organisms that destroy the mucosal lining of the intestines, producing pus, blood and mucus in stool
• Osmotic diarrhea


  Caused by inefficient reabsorption of an osmotic substance due to an enzyme deficiency, resulting in the retention of water and electrolytes in the large intestine
• Causes of osmotic diarrhea

  • Lactose intolerance
  • Pancreatic insufficiency
• Altered motility


  Conditions of enhanced motility (hypermotility) or slow motility (constipation), can be seen in irritable bowel syndrome (IBS)
• Steatorrhea


  Increase in fat in stool (>6g/day) due to absence of bile salts that assist pancreatic lipase in the breakdown and subsequent reabsorption of triglycerides
• Conditions associated with steatorrhea

  • Pancreatic disorders (cystic fibrosis, chronic pancreatitis, carcinoma that decrease the production of pancreatic enzymes)
• 1. xylose test


  Distinguishes steatorrhea in maldigestion and malabsorption conditions by measuring the absorption of a sugar that does not need to be digested
• Macroscopic examination

  • Color
  • Consistency
  • Form
• Macroscopic screening: color


  Normal brown color, pale color signifies biliary obstruction, black/tarry stools indicate upper GI bleeding, red stools indicate lower GI bleeding, green stools can be caused by biliverdin, oral antibiotics, or green vegetables
• Macroscopic screening: consistency


  • Formed
  • Hard
  • Watery
• Macroscopic screening: form

  • Cylindrical (normal)
  • Ribbon-like (intestinal strictures)
  • Small, round/scybalous (constipation)
  • Bulky and frothy (steatorrhea)
  • Mucoid (colitis, constipation)
• Odor


  Depends on the pH of the stool and substances produced by intestinal bacterial fermentation and putrefaction, a foul odor is caused by degradation of undigested protein and excessive carbohydrate intake, a sickly sweet odor is produced by undigested lactose
• Fecal occult blood


  Hidden blood, not seen by microscopic examination, normally found in small amount, screening test for colorectal cancer and GI tract bleeding
• Principle of fecal occult blood test

  Based on the pseudoperoxidase activity of hemoglobin molecule reacting with the chromogen, gum guiac is commonly used as it is not too sensitive to avoid high false positives
• Conditions associated with abnormal stool

  • Pancreatic insufficiency
  • Intestinal constriction due to malignancy (colon cancer)
  • Amoebic colitis
  • Dysentery
  • Malignancy
• Odor of stool


  • Depends on the pH of the stool and indole and skatole are the substances that produce normal odor formed by intestinal bacterial fermentation and putrefaction
  • A foul odor is caused by degradation of undigested protein and excessive carbohydrate intake
  • Sickly sweet odor is produced by undigested lactose
• Fecal occult blood


  • Hidden blood, not seen by microscopic examination
  • Normally found in small amount, 2.5ml/ 150 grams of stool
  • Screening test for colorectal cancer & GIT bleeding
  • Significant if > 2.5ml/ 150 grams of stool
• Principle of fecal occult blood test

  Based on the pseudoperoxidase activity of hemoglobin molecule reacting with the chromogen
• Chromogens used


  • Gum guiac
  • Benzidine
  • O-tolidine
• Positive result of fecal occult blood test

  Blue chromogen
• Substances that may exhibit pseudoperoxidase activity/reaction

  • Hemoglobin
  • Myoglobin
  • Vegetables
  • Fruits
  • Red meat
  • Horse radish
  • Melons
  • Raw broccoli
  • Turnip
  • Vitamin C
  • Iron
• Causes of false positive fecal occult blood test

  • NSAIDS
  • Contamination of menstrual blood
  • Hemorrhoids
• Causes of false negative fecal occult blood test

  • Non adherence to diet advice
  • Vitamin C and Iron intake
• Immunochemical fecal occult blood test (iFOBT)


  • Specific for globin portion of human hemoglobin, uses anti-human hemoglobin antibodies
  • Does not require dietary or drug restrictions
  • More sensitive to lower GI bleeding that could be an indicator of colon cancer or other GI disease and can be used for patients who are taking aspirin and other anti-inflammatory medications
• Porphyrin-based fecal occult blood test (Hemoquant)


  • Offers a fluorometric test for hemoglobin based on the conversion of heme to fluorescent porphyrins
  • Measures both intact hemoglobin and the hemoglobin that has been converted to porphyrins
• APT test


  • Determines if infant's stool or vomitus is fetal or maternal in origin
  • Fetal blood resists alkali denaturation (remains pink) while maternal blood is sensitive to alkali denaturation (yellow brown)
• Procedure of APT test


  Specimen emulsified with water, centrifuged then added with 1% NaOH
• Result of APT test

  • Maternal blood is denatured = yellowish brown
  • Fetal blood is unchanged = pink
• Quantitative fecal fat testing

  • Confirmatory test for steatorrhea
  • Collection of 3 day fecal specimen
  • Method: Van de Kamer titration (gold standard)
  • Rapid test: Acid steatocrit