Examination of fecal matter that provides important information to aid in the differential diagnosis of various disorders and conditions of the gastrointestinal tract
Conditions that can be assessed using stool
Maldigestion
Malabsorption
Gastrointestinal tract malignancies
Hepatic and biliary conditions
Infectious diseases commonly caused by parasites
Pancreatic diseases
Laboratory evaluation of feces
Encompasses macroscopic, microscopic, and chemical examinations
Fecal formation
1. Small intestine is the primary site for final breakdown and reabsorption of ingested proteins, carbohydrates and fats
2. Undigested and unreabsorbed material is passed to the large intestine
3. Undigested material is moved throughout the large intestine at a relatively slow rate (18-24 hours)
4. Large intestine is capable of absorbing about 3000 mL of water, final fecal product normally contains only about 100 mL of fluid
Diarrhea
Increase in the volume, fluidity and frequency of bowel movements
Types of diarrhea
Secretory diarrhea
Osmotic diarrhea
Intestinal hypermotility diarrhea
Secretory diarrhea
Results from increased intestinal secretion of fluid and electrolytes into the large intestines, commonly due to bacterial, viral, and protozoan infections, as well as other causes
Osmotic diarrhea
Results from the ingestion of an osmotically active solute which is incompletely broken down in the small intestine, causing water and electrolytes to be retained in the large intestine instead of being reabsorbed
Intestinal hypermotility diarrhea
Transit time for intestinal contents is too short to allow normal intestinal absorption to occur
Fecal osmolality
Used to differentiate between secretory and osmotic diarrhea
Steatorrhea
Increase in stool fat, exceeding 6-7 grams per day, useful for diagnosis of pancreatic insufficiency and small bowel disorders that cause malabsorption and maldigestion
Steatorrheic stools
Pale, greasy, bulky, spongy, or pasty and extremely foul-smelling, may float or be foamy due to large amounts of gas present
Specimen collection
1. Patients should collect specimen in a clean container and transfer a small amount to the designated laboratory container
2. For quantitative testing, timed specimens collected over 3 days are necessary
Chemical examination (occult blood, fecal fat, carbohydrates, enzymes, APT test)
Macroscopic examination of stool
Changes in color and formed consistency can indicate gastrointestinal disturbances, differentiated from changes due to ingestion of pigmented food and drugs
Stool color
Brown (normal)
Pale/white/gray (bile duct obstruction)
Black/tarry (upper GI bleeding)
Red (lower GI bleeding)
Green (antibiotic use, increased green vegetables)
Mucus-coated - intestinal irritation or inflammation
Red-colored stools
Caused by certain medications (e.g. rifampin)
Pale yellow, white, gray stools
Due to bile-duct obstruction (when no bile is passing to the intestines), barium sulfate
Green stools
May be seen in patients taking oral antibiotics due to the oxidation of fecal bilirubin to biliverdin, and also with increased intake of green vegetables or food coloring
Diarrhea
Stools can be excessively watery
Constipation
Stools are characteristically hard and small
Slender, ribbon-like stools
Suggest an obstruction of the normal passage of fecal material through the intestine
Steatorrheic stools
Appear bulky and frothy, frequently have a foul odor, may also appear greasy and may float in water
Mucus-coated stools
May be indicative of intestinal irritation or inflammation or they may also be caused by excessive straining during evacuation (either a physiologic or psychological origin)
Fecal leukocytes
Leukocytes, primarily neutrophils, are seen in the feces in conditions that injure the intestinal mucosa such as ulcerative colitis and bacterial dysentery
Screening for leukocytes
An important preliminary test to determine whether a patient's diarrhea is being caused by invasive bacterial pathogens that produce enterotoxins
Undigested striated muscle fibers
Can be helpful in the diagnosis and monitoring of patients with pancreatic insufficiency
Protein in muscle fibers is not broken down because the pancreas fails to secrete the enzymes needed for its digestion
Increased amounts of striated muscle fibers
May also be seen in gastrocolic fistulas
A fistula is an abnormal communication between two organs. In this case (gastrocolic) there is an abnormal communication between the stomach and the large intestine so that any undigested fibers in the stomach directly goes to the large intestine so undigested muscle fibers are seen in the stool
Presence of >10 per HPF
Considered as increased
Increased amounts of fat in fecal specimens
May be seen in pancreatic insufficiency or biliary obstruction, conditions wherein dietary fat is not broken down efficiently
Biliary obstruction is also implicated because (aside from lipase in pancreatic secretions), bile salts are also needed to digest fat
Qualitative fecal fats
Can be used to monitor patients undergoing treatment for malabsorption disorders
Types of lipids included in the microscopic examination
Neutral fats (triglycerides)
Fatty acid salts (soaps)
Fatty acids
Cholesterol
Staining for fat compounds
Samples are stained with dyes such as Sudan III or IV or Oil Red O
Microscopic evaluation
Used to look for parasitic ova
A vast majority of the parasitic ova are detectable through the stool exam