Fecal

normal composition of feces

75% water and remaining solid fraction contains

• bacteria

• protein

• carbohydrates

• undigested plant matter

• fat

analysis of fecal matter is to have early detection of —

• GI bleeding

• liver and biliary duct disorders

• maldigestion or malabsorption

• inflammation

• presence of parasites or bacteria

collecting fecal specimen

• in a clean container and transferred to lab container

• avoid contamination with urine

• three day collection

types of diarrhea

secretory and osmotic

secretory diarrhea

caused by increase water and electrolyte secretion

osmotic diarrhea

caused by poor absorption because of osmotic pressure

• water is not reabsorbed in colon

common tests for secretory diarrhea

• stool culture

• ova and parasite examinations (O&P)

• rotavirus immunoassay

• fecal leukocytes

common tests for osmotic diarrhea

• microscopic or quantitative fecal fats

• muscle fiber detection

• qualitative fecal fats

• trypsin screening

• clinitest for carbohydrates

brown feces

normal - caused by urobilin in stool (urobilinogen → urobilin)

black feces

aka melena - caused by upper GI bleeding, iron therapy, charcoal ingestion, or certain medications

red feces

caused by lower GI bleeding, some foods, dyes, or drugs

pale or clay colored feces

aka acholic feces - caused by barium or post-hepatic obstruction of bile ducts which inhibits urobilin production

green feces

caused by biliverdin following antibiotic therapy or ingestion of green vegetables

bulky or frothy feces

steatorrhea - caused by excess fat in stool or pancreatic disorder

ribbon-like feces

caused by obstruction of normal flow

mucus/blood streaked feces

caused by inflammation of intestinal wall - colitis, dysentery, malignancy

fecal leukocyte testing

looks for lactoferrin which indicates neutrophils in feces

• increase associated with ulcerative colitis, bacterial dysentery, invasive bacterial infections

• can also use methylene blue to stain

qualitative fecal fats

performed to determine presence of excess fecal fats and monitor patients with malabsorption disorders

stains used in qualitative fecal fats

Sudan III or Oil red O

neutral fats (trigs) in qualitative fecal fats stain as—

large orange-red ddroplets

cholesterol in qualitative fecal fats stain as—

crystals after heating and cooling

fatty acid salts (soaps) in qualitative fecal fats stain as—

large droplets after slide is heated and acetic acid is added

most common fecal test performed is—

occult blood test

occult blood test can pick up blood that is —

not observed macroscopically in stool

occult blood testing screens for —

colorectal cancer

chemical used in occult blood test

guaiac (gFOBT) is inoculated with feces and H₂O₂ is added

mechanism of reaction in occult blood test

pseudo-peroxidase activity of hemoglobin converts H₂O₂ to water and oxidizes the guaiac (chromogen) to form a blue color change