CS II 2.3: Fecal Analysis

What are some of the natural protective mechanisms of the GI tract against infection?

• Increased acidity of the stomach

• rapid transit time of the small bowel

• ileocecal valve inhibits bacteria from the large intestine from moving backwards

• normal flora (inhibit growth of new bacteria)

What are some osmotic causes of diarrhea? Does fasting improve sxs?

Lactose intolerance, increased sorbitol; yes - diarrhea volume will decrease if you stop consuming the items

What are some secretory causes of diarrhea? Does fasting improve sxs?

Endocrine disorders, Zollinger-Ellison syndrome, laxatives, bile salt malabsorption; no - diarrhea volume will not decrease if you stop consuming the items

What are some fast & slow motility disorder causes of diarrhea, respectively?

Fast: reduced contact (hyperthyroid, s/p gastrectomy, IBS)

Slow: bacterial overgrowth (hypothyroid, DM, scleroderma)

What are is the difference between the appearance/contents of inflammatory vs. noninflammatory diarrhea?

Inflammatory: outpouring of necrotic tissue, colloid, fluid, electrolytes, & blood

Noninflammatory: excessive secretion of electrolyte w/o blood or pus

How should stool samples be collected?

In a bed pan/hat & then transferred to sterile containers (cannot contain urine, toilet paper, or toilet water)

What is the difference between malabsorption and maldigestion?

Malabsorption: reduced absorptive capability & fast transit time (patient often has steatorrhea due to ↓ fat absorption)

Maldigestion: food cannot be digested usually due to secondary obstruction in the pancreatobiliary tree or small bowel (tumor, gallstones, etc.)

Overall, what is fecal fat testing used for?

Evaluate patients w/ steatorrhea by measuring fecal fat content over 3 days

What are some things that can cause increased & decreased fecal fat levels, respectively?

Increased: CF, malabsorption (Celiac, Crohn's, etc.), maldigestion (obstruction of some kind), short gut syndrome, enema use, laxative use (mineral oil)

Decreased: recent barium administration, fiber laxatives/supplements

What does D-xylose absorption measure, & what is it useful for?

Evaluates the absorptive capability of the intestines - can d/dx malabsorption from maldigestion (D-xylose absorption diminished in malabsorption)

How are D-xylose levels measured?

Baseline serum & urine amounts are taken; serum levels collected again at 1 hr (peds) or 2 hrs (adults) while urine levels are collected again at 5 hrs

How many samples are required for a stool ova & parasite? What kinds of organisms can this test help ID?

Minimum of 3 over the course of ten days (every other day); worms & parasites

What kinds of organisms can a stool culture help ID? What else does this test do?

Common bacterial etiologies; isolation of the microbe for ID & antibiotic sensitivity

What is the gold-standard test for identifying C. difficile infection? What is an alternative we can do?

Gold-standard = toxigenic stool culture; alternative = stool EIA for toxin A & B (rapid but less sensitive)

What is the gold-standard test for identifying Salmonella?

Stool culture

What is the gold-standard test for identifying Shigella?

Stool culture

What is the significance of enterohemorrhagic E. coli?

This subtype produces a toxin called "Shiga toxin" that can cause bloody diarrhea & hemolytic uremic syndrome - this can be fatal

How are all subtypes of E. coli (enterohemorrhagic, enteropathogenic, & enterotoxigenic) diagnosed? What is something that can be specifically done to diagnose the enterohemorrhagic type?

Stool culture; Shiga toxin EIA

How is norovirus usually diagnosed?

Usually clinical (since sxs often self-resolve within a day), but if a test is needed PCR is used the most

How is rotavirus usually diagnosed?

Rapid antigen testing is most common

How is Giardia diagnosed?

Ova & parasite evaluation

How is Enterobius (pinworm) usually diagnosed?

Ova & parasite is the best test, but the tape test can also be done & usually works pretty well

Who does Cryptosporidium usually affect? How is this usually diagnosed?

Immunocompromised patients; ova & parasite w/ special stain (need to specifically indicate you are testing for crypto)

What is a great first-line test to diagnose Celiac disease? What is the gold-standard test that we need to follow this up with?

Serology in the form of an anti-tissue transglutaminase (anti-tTG) panel; small bowel biopsy = gold-standard