7. Fecal Analysis Flashcards
normal adult excretes —– g/day of feces
100-200 g
4 major digestive enzymes from pancrease
- trypsin
- chymotrypsin
- amino peptides/elastase
- lipase
aid in fat digestion
bile salts from liver
—– mL enters GI tract each day
9000 mL
fecal electrolyte content is similar to that of…
plasma
large intestine can absorb around —— mL water
3000 mL
diarrhea definition (3)
- increase in daily stool weight > 200g
- liquidity
- frequency of > 3x/day
chronic diarrhea
> 4 weeks
3 major mechanisms of diarrhea
- secretory
- osmotic
- intestinal hypermotility
——— = 290 - [2(fecal Na) + (fecal K)]
osmotic gap
osmotic vs secretory diarrhea
osmo gap
osmotic: ↑ (> 50)
secretory: ↓ (< 50)
osmotic vs secretory diarrhea
fecal Na
osmotic: ↓ (< 60 mmol/L)
secretory: ↑ (> 90 mmol/L)
osmotic vs secretory diarrhea
fecal K
osmotic: ↓ K
osmotic vs secretory diarrhea
pH
osmotic: ↓ (< 5.3)
secretory: ↑ (> 5.6)
osmotic vs secretory diarrhea
reducing substance
osmotic: +
secretory: =
osmotic vs secretory diarrhea
stool output
osmotic: ↓ (< 200 g)
secretory: ↑ (> 200 g)
secretory diarrhea
increased secretion of water
overrides absorptive ability
often infections (enterotoxin-producing—think cholera)
osmotic diarrhea
poor absorption that exerts osmotic pressure across intestinal mucosa
water and electrolyte retention
malabsorption and maldigestion contribute to ——– diarrhea
osmotic
osmotic diarrhea causes
lactose intolerance
laxatives
Mg-containing antacids
amebiasis
antibiotics
intestinal motility is altered by…
dietary fiber
chemicals
nerves
hormones
emotions
nerves and muscles of the bowel are extra sensitive
IBS
causes of hypermotility
enteritis
parasympathetic drugs
complications of malabsorption
secretory & osmotic diarrhea
causes of constipation
diet
↓ exercise
↓ water, fiber
dairy products
antacids
resisting the urge
stress
long term laxative use
pain medications
IBS
pregnancy
etc
fecal fat
steatorrhea
absence of bile salts gives > — g/day of fecal fat
6 g
pale, greasy, bulky, spongy, pasty foul stools
steatorrhea
differentiates malapsorption from pancreatitis as causes of steatorrhea
D-xylose test
low urine D-xylose after ingestion
malabsorption condition
no D-xylose in blood after ingestion (normal)
pancreatitis
3 colorless tetrapyrroles
(general name)
urobilinogens
conjugated bilirubin –> intestinal bacteria –> urobilinogens
3 urobilinogens
- urobilinogen
- stercobilinogen
- mesobilinogen
what happens to urobilinogens in the lower GI tract?
spontaneously oxidized to bile pigments (“bilin” form)
orange brown color
black stool
upper GI bleed
iron therapy
charcoal
bismuth
red stool
lower GI bleed
beets
rifampin
pale yellow, white, gray stools
bile duct obstruction
barium sulfate
green stools
biliverdin
oral antibiotics
green veg
claylike white stools
bile duct obstruction
pancreatic disorders
ribbonlike stools
intestinal constriction
mucus/bloody mucus in stools
colitis
dysentery
malignancy
constipation
—- WBCs/hpf indicates invasive, inflammatory condition
1-3
——– bacteria are usually the cause of fecal leukocytes
invasive
(not toxin producing, viruses or parasites)
methods for detecting fecal WBCs (3)
wet prep + methylene blue (fresh specimen)
dried smear + wright/gram stain (fresh specimen, permanent slides)
lactoferrin latex agglutination (refrigerated/frozen specimen)
muscle fiber examination useful in diagnosing… (3)
- pancreating insufficienty (CF)
- biliary obstruction
- gastrocolic fistulas
——– slides are used for muscle fiber exam
emulsification
muscle fiber exam
emulsify stool in —- drops of ———
2 drops
10% alcoholic eosin
muscle fiber exam
only count…
undigested fibers
vertical and horizontal striations
> 10 is reported as increased
2 parts of qualitative fecal fat exam
why?
- neutral fat stain—only neutral fats
- split fat stain—also stains fatty acid salts (soaps), fatty acids, cholesterol
neutral fat stain
water
95% ethyl alcohol
Sudan III
split fat stain
acetic acid
Sudan III
how to quantify fats for both types of stain
- neutral: large orange droplets/HPF
- split: all orange droplets/HPF
steatorrhea indicated by each stain’s droplet count
- neutral: > 60/HPF
- split: > 100/HPF
normal neutral stain count
elevated split stain count
malabsorption
elevated neutral and split stain count
maldigestion
detects early stages of colorectal cancer
FOBT
amount of occult blood that is clinically significant
2.5 mL/150 g
3 FOBT methods
- Guaiac-based FOBT
- Immunochemical FOBT
- Porphyrin-based FOBT
point of care FOBT
guaiac
gFOBT relies on the ——– of hemoglobin
pseudoperoxidase
gFOBT false positives
red meats (myoglobin)
horseradish, melons, broccoli, cauliflower, radishes, turnips
aspirin, NSAIDs
rehydration of dried sample prior to developer
gFOBT false negatives
vitamin C
failure to wait for sample to dry
iFOBT relies on the ——— of hemoglobin
globin portion (anti-human Ab)
FOBT with no dietary or medication restrictions
iFOBT
porphyrin FOBT relies on…
conversion of heme to fluorescent porphyrins
FOBT more sensitive to upper GI bleeds
porphyrin
porphyrin FOBT false positives
red meat
confirmatory, quantitative fecal fat test
3-day collection
coefficient of fat retention and reference value
100[(dietary fat - fecal fat)/dietary fat] = coefficient of fat retention
should be at least 95%
5 methods of measuring fat in a 3-day collection
time consuming
- Van de Kamer titration (gold standard)
- gravimetric
rapid
- near-infrared reflectance spectroscopy
- NMR
- acid steatocrit
VDK titration gets —-% of fecal fat
80%
test to find out if blood in neonate stool is from them or from swallowing mom’s
APT test (fetal hemoglobin)
positive for fetal hemoglobin
remains pink after alkali treatment (1% NaOH)
(mom’s Hgb will denature)
3 fecal enzyme tests
- trypsin (not used)
- chymotrypsin (not used)
- elastase 1
elastase 1 test is an ——- test
ELISA
CHO in stool produces —— diarhhea
osmotic
2 examples of what can cause CHO in feces
Celiac
lactose intolerance
test for CHO in stool
Clinitest
screening only; needs to be confirmed with serum test
pH < —– can correlate with + stool clinitest
5.5
