Fecal Flashcards
Small intestine function
- Break down and absorption: fats, carbohydrate, proteins
- Aided by enzymes: pancreas (trypsin, chymotrypsin, aminopeptidase, lipase), liver (bile salts)
Large intestine function
- Reabsorption of water: up to 3L (normally 500mL-1.5L), 150ml excreted in feces/9L total
- Bacteria: GI flora: creates vitamins (K, B12, etc.) and flatus (gas)
- Feces: compacts and stored in the rectum until excretion
Fecal sample collecting
- Clean container & avoid contamination with urine for chemistry and O&P
- Fecal occult blood kit
- Material on gloves for examination
- Rectal swab for infants
- Random stool: Qualitative testing and microscopy: Leukocytes, muscle fibers, and fecal fats
- 72 hrs stool: Quantitative testing for fecal fats (high-fat diet to prepare), multiple containers.
Fecal characteristic
100-200g/day
pH: 6.5 - 7.5
Osmolality: 290 mOsm/kg
Normal: tubular or cylindrical
Fecal appearance - abnormal
Bulky, frothy: bile-duct obstruction, pancreatic disorder
Ribbon-like: Intestinal constriction
Mucus-coated: intestinal inflammation
Blood streaking: damage to the intestinal wall, dysentery, malignancy, constipation.
Fecal appearance - color
- Brown: normal - oxidation of stercobilinogen to urobilin
- Black, tarry: upper GI bleeding: must test blood chemical, takes 3 days to appear in the stool
- Red: lower GI bleeding: must test for blood chemical
- Green: oral antibiotic, biliverdin
- White: bile duct obstruction
Diarrhea
- Incr daily stool weight, liquidity, frequency
- Secretory: incr secretion of water
- Osmotic: poor absorption –> incr osmotic pressure –> incr water loss through diffusion
- normal fece: Na (30mmol/L), K (75mmol/L), Osmolality (290mOsm/kg)
Osmotic diarrhea
Osmotic gap > 50 Osm/kg –> incr osmolality
Na < 60
Output < 200g
pH < 5.3
Reducing substances: Pos
Cause:
- Incomplete breakdown: disaccharidase deficiency, celiac sprue
- Malabsorption: laxative, Mg-containing antacids, antibiotic. Consuming a large amount of carbohydrate
Secretory diarrhea
Osmotic gap < 50 Osm/kg Na > 90 --> incr electrolytes secretion Output > 200g pH > 5.6 Reducing substance: Neg Cause: - Pathogenic infection - Medication, stimulant laxatives - Endocrine disorder - Bowel inflammation, neoplasm, collagen vascular disease.
Steatorrhea
- Fecal fat
- Malabsorption & Maldigestion
- 2 slide tests (qualitative):
+ Neutral fat stain (Sudan III) –> fat content: > 60drops: Pos
+ Split fat stain (acetic acid + heating) –> total fat –> droplet larger than 4um: Pos
Malabsorption
- Increased total fat and neutral fat
- Low urine D-xylose (As D-xylose is not digested but absorbed and secreted in urine)
- Cause: Pathogenic infection, celiac sprue, lymphoma, whipple dz, intestinal ischemia
Maldigestion
- Increased neutral fat only
- Normal urine D-xylose
- Cause: Absence of bile salt (pancreatic lipase reduced), chronic pancreatitis, carcinoma, cystic fibrosis
Fecal occult blood testing
- Detection: invisible bleeding: > 2.5mL/150g stool, annual screening for colorectal cancer
- 3 methods:
+ gFOBT: hemoccult
+ iFOBT: FIT
+ porphyrin-based FOBT: HemoQuant
gFOBT (Guaiac)
- Same with a blood test on UA (blue: pos)
- Limitation:
+ Dietary restriction (avoid red meat, horseradish, watermelon
+ False-pos from aspirin and anti-inflammatory
+ Contamination - False-negative: vitamin C
iFOBT (Immunology)
- Use anti-human hemoglobin Abs
- Sensitive to lower GI bleeding: colon cancer or GI dz, decrease false pos, blood from GI is active
- Can be used for pt taking aspirin and anti-inflammatory
porphyrin-based FOBT
- Based on convert heme to fluorescent porphyrins
- Sensitive to upper GI bleeding
- Unaffected by redox agent and water
- Limitation: no red meat 3 days prior testing
Quantitative Fecal Fat Testing
- Confirmation test for steatorrhea
- At least 3-day specimen: intake fat regularly, refrigeration prevents bacterial degradation.
Van de Kamer testing
- Gold standard
- Fecal lipid –> fatty acids –> neutral endpoint
- 80% of total fecal content
- Limitation: time-consuming, corrosive and flammable solvents
Gravimetric
- Measure all fecal fat
- Limitation: time-consuming, corrosive and flammable solvents
Hydrogen Nuclear Magnetic Resonance Spectroscopy
- Rapid & safe
- Microwaved -dried and analyzed
- Fat content = gram of fat per 24 hrs
- 1-6 g/d for 100g/d intake
Acid steatocrit
- Rapid test
- Estimates amount of fat excretion
- Similar to microhematocrit
- More convenient than 72-hrs stool collection
- Monitor pt’s response
- Steatorrhea in children
Near-Infrared Reflectance Spectroscopy
- Rapid
- Less stool, but requires 48-72 hrs collection
- Computed processing of signal data from reflectance of the fecal surface.
+ Infrared light between 1400nM & 2600nM
+ calculated from calibration from known sample
Increased neutrophilia in stool
- Inflammation
- Infection causes diarrhea
+ Invasive bacteria: exhibit leukocytes in fecal
+ Toxin production: NOT exhibit leukocytes in fecal
Neutrophilia in stool - test
- Wet mount with methylene blue (fast)
- Gram stain
- Lactoferrin latex agglutination
- 3 cells/hpf –> pos
Fecal Microbiota Transplant
- Treatment for C. difficile colitis
- Suspect if > 3 water stools in 24 hrs + history of antibiotic treatment
- A cure rate of 91-96%
Fecal Microbiota Transplant - Methods
- Nasogastric tube: deliver to small bowel
- Colonoscopy: deliver directly to C. difficile found
- Frozen FMT capsule
Fecal transplant - Lab role
- Testing for antigen/enzyme IA, serology, molecular assay for common bacteria, viruses, and parasite
- Blood test: cells count and liver function panel
- Stool test: O&P, C.difficile has high asymptomatic carriers (enzyme immunoassay for toxin, molecular assay)
