MIDTERMS | Fecalysis

• Feces


  An end product of body metabolism
• Contents of feces

  • Bacteria
  • Cellulose
  • Undigested food stuffs
  • Gastrointestinal secretions
  • Bile pigments
  • Cells
  • Electrolytes
  • Water
• All undigested materials are contained in feces
• Around 100-200g of feces is excreted in 24hour period
• Two most common reasons to collect a fecal specimen

  • To look for intestinal infection (parasitic or bacterial)
  • Screen for colorectal cancer
• Normal brown color of feces


  Results from intestinal oxidation of stercobilinogen to urobilin
• Changes in stool color may be due to

  • Diet
  • Drug intake
  • Underlying medical conditions
• Black/tarry stool


  Blood originates from the esophagus, stomach or duodenum (Upper GI tract)
• Red stool


  Blood originates from lower GI tract
• Bilirubin


  Hemoglobin degradation (goes to urine and stool)
• Bulky-frothy stool


  Bile salts + lipase is important in breaking fats from food. If bile salts or lipase can't mix with food, fats are not broken down.
• Mucus in stool


  Indicates inflammation or irritation of intestine (e.g. Colitis, dysentery, suspected presence of amoeba)
• Rifampin


  Antibiotics to TB
• Random specimen


  Used for most determinations, including bacterial cultures, ova and parasites and fats and fibers. No specific time, pea size.
• Occult Blood specimen


  Collected after 3 days of a meat-free diet. Patients are instructed to avoid certain foods and medications that can interfere with the test.
• 72 Hour Stool specimen


  Rarely called for and is ordered when a random specimen is positive for excess fat. Used for quantitative fecal fat determination.
• Fecal specimen container


  Screw-cap sterile container. Patients should be instructed to defecate into it, not the toilet, and avoid urine contamination.
• Steatorrhea


  Increased fecal fat, useful in diagnosing pancreatic insufficiency and small-bowel disorders that cause malabsorption
• Creatorrhea


  Abnormal excretion of muscle fibers in feces, caused by biliary obstruction
• Fecal leukocytes


  Leukocytes, primarily neutrophils, seen in the feces in conditions that affect the intestinal mucosa
• Microscopic screening for diarrhea

  Preliminary test to determine whether a diarrhea is being caused by invasive bacterial pathogens or by bacterial toxin production
• Tropozoid

  Entamoeba hestolitica (protozoan causative agent for amoebiasis), looks like a huge RBC
• Tests for amoebiasis

  • Detection of Antigen
  • ELISA (Enzyme-link Immunosorbent Assay)
• Diarrhea


  Defined as an increase in daily stool weight above 200g per day with increased liquidity and frequency of more than 3 times a day. Acute diarrhea can last up to less than 4 weeks, chronic diarrhea lasts more than 4 weeks.
• Mechanisms of diarrhea

  • Secretory
  • Osmotic
  • Altered motility
• Secretory diarrhea


  Caused by increased secretion of water and electrolytes which override the reabsorptive ability of the large intestine. Normal large intestine physiology is to absorb electrolytes and water back. Osmotic gap of <50 Osm/kg.
• Causes of secretory diarrhea

  • Bacterial infection
  • Viral infection
  • Protozoan infection
  • Laxatives (not recommended)
  • Hormones
  • Inflammatory bowel disease
• Osmotic diarrhea


  Caused by increased retention of water and electrolytes in the large intestine due to incomplete breakdown or reabsorption of food. Osmotic gap of >50 Osm/kg.
• Causes of osmotic diarrhea

  • Maldigestion- impaired food digestion
  • Malabsorption- impaired nutrient absorption by the intestine
  • Lactose intolerance
• Osmotic gap

  Calculated as 290 - [2 (fecal sodium + fecal potassium)], used to differentiate secretory and osmotic diarrhea
• Occult blood in stool


  Bleeding in excess of 2.5mL/150g of stool is considered pathologically significant, even if no visible signs of bleeding
• Fecal Occult Blood Test (FOBT)


  Necessary for the detection of hidden blood in stool, based on the pseudoperoxidase activity of hemoglobin
• Annual testing for occult blood has a high predictive value for detecting colorectal cancer in early stages (recommended for age >50 by American Cancer Society)
• Foods and medications to avoid 3 days before FOBT specimen collection


  • Red meats
  • Horseradish
  • Melons
  • Raw broccoli
  • Cauliflower
  • Radishes
  • Turnips
• Guaiac-based FOBT

  Most frequently used screening test for fecal blood, based on detecting the pseudoperoxidase activity of hemoglobin
• Immunochemical Fecal Occult Blood Test

  Specific for human blood in feces, no false positives/negatives since it detects human blood directly
• Interpretation of FOBT results

  • iFOBT: Reagent, 2 lines (+), 1 line in Control (-), No line in Control (void)
  • gFOBT: Presence of blue (+)
• • Type 1: Separate hard lumps like nuts (hard to pass)
• Type 2: Sausage shaped but lumpy
• Type 3: Like sausage but with cracks